The genera Cruziturricula and Fusiturricula form an unsupported group that is sister to Drilliidae. In the studied Cruziturricula arcuata (Reeve, 1843), the very characteristic radula differs from the Drilliidae: 1-0-0-0-1. Marginal teeth are loosely enrolled with little overlap of the edges, with two barbs on the tip and a tongue-shape extension at the base. The type species of Fusiturricula, Turris fusinella Dall, 1908, is different from what is currently conceived as belonging to that genus (e.g. Williams, 2006), but those species are similar to Cruziturricula sensu aucct. The only data on the radula was provided by Powell (1966: 31), who stated (without mentioning the species): "Radula of marginals only, wish bone-type, but long and narrow"'. Although Cruziturricula and Fusilurricula definitely do not belong in Drilliidae and may represent a new family, they are here provisionally placed in Drilliidae for lack of a better alternative.

Shell small- to medium-sized, usually 15-25 mm, up to 50 mm high, with a rather high spire and usually truncated base. Spiral sculpture often obsolete. Anal sinus on subsutural ramp, deep, (sub)symmetrical, sometimes tubular. Protoconch usually paucispiral (up to two whorls), smooth or abapically carinate. Operculum with terminal nucleus. Radular formula 1-1-R-1-1, rarely 1-1-0-1-1, central tooth small, from narrow unicuspid to subrectangular with additional cusps, rarely reduced to completely absent. Lateral teeth broad, pectinate, and arched, marginal teeth from simple flat and sharply pointed to duplex with slightly thickened edges and to loosely enrolled with the small barb near the tip (Imaclava).

Description of shells in the family of Drilliidae. With the exception of the single new genus, all diagnoses of genera are based on those published by the original author, modified where necessary to clarify and standardize them for ease of comparison; i.e., shell surface microsculpture was not always perceived as particularly important by past researchers but is an important characteristic that is apparently conserved at the genus level among the TWA Drilliidae. A few generic reassignments were necessary but were expected given the confusion about the definition of some genera and the importance of certain characters that define the genus. Clarification of TWA genera was important to allow proper placement of the new species described in this work and will hopefully suffice for future additions. It is also expected that the results of this morphological work will aid in the experimental design of future anatomical and molecular work.
A brief glossary of the terminology used to describe shell morphology follows. Since it differs slightly among describers, it felt that an explanation of the terminology used in this work would be helpful.
Shell gross morphology is described as either fusiform (spindle-shaped), or fusiform with truncated anterior (claviform), and includes maximum whorl count of largest specimen examined, including protoconch whorls, and whorl profile. The description of the whorl profile may include the degree of convexity, and the length of last whorl as a percent of total shell length including anterior canal. Shell sizes are arbitrarily categorized on the basis of total length: very small (=< 10 mm), small (> 10 mm < 25 mm), medium (> 25 mm and < 50 mm) or large (> 50 mm). W/L ratio, or width to length ratio, is a useful measure to describe the degree of stoutness or spindliness, especially between genera that exhibit extremes of the two. Cerodrillia, which has a stout profile, has a W/L ratio usually greater than 0.4, while Leptadrillia, which is spindly, is usually less than 0.4.
Protoconchs are mostly smooth, without sculpture, and range IV2—3 whorls in size but differences among species are found in relative size, form, and texture (glossy or opaque). Although lacking ornamentation, protoconchs have subtle differences that may be diagnostic at the species level; a few differences occur even at the generic level such as exemplified in separating Calliclava (two carinate whorls) from Clathrodrillia (two smooth whorls), or separating some species within a genus that may have either 2- or 3-whorl protoconchs (Cerodrillia and Douglassia). Differences in form are seen in whether the first whorl is free (end, side and top of the first whorl is visible), partially immersed in the second (only top is visible), or impressed, as if the tip of the first whorl was pressed into the second as into a lump of clay. More than one form (free, impressed or immersed) is observed in species of the same genus, so this character does not have diagnostic value at the genus level.
Axial ribs are the most dominant sculptural element of the drilliid shell, their form often diagnostic at the genus and sometime species level within some genera. They may be present from suture-to-suture on spire whorls, (Bellaspira, Cerodrillia, Decoradrillia, Leptadrillia, Lissodrillia, Syntomodrillia), weakened or narrowed and recurved but present in the sulcus nonetheless (Agladrillia, Bellaspira, Clathrodrillia, Fenimorea, Neodrillid), or terminate at the sulcus (Splendrillia). Ribs may be oblique (usually opisthocline), sigmoid, or straight. Rib counts are variable but ranges are given for the penultimate and last whorls when useful to distinguish species in a qualitative way. Rib count on the last whorl is made from the first rib that clears the parietal callus to the rib adjacent to the varix. The varix is not counted, nor is the number of post-varical axial folds. Ribs may also differ in cross-sectional form, some rib crests are ridged, and others are round.
Sulcus is the region on the whorl shoulder just below the suture influenced by the progression of the shell's anal sinus. It may lack sculptural elements, as in Splendrillia, or have axial ribs reduced by varying degrees, depending on the species. Frequently axials are recurved as they near the suture, reflecting the outline of past positions of the anal sinus. A few genera have little or no reduction or distortion of axials in this region (some Cerodrillia, Decoradrillia, Leptadrillia, Syntomodrillia, and Lissodrillid).
Anal sinus can be very shallow, marked by a slight indentation of the edge of the outer lip beginning at the suture (Bellaspira), reverse L-shaped where the outer lip joins the suture behind the parietal lobe (Splendrillia), or U-shaped, usually deep, sides parallel, divergent, or convergent (Lissodrillid). The sinus can be spout-like in mature specimens of some genera because the inner edge of the sinus is flared up, and outer lip curved outward such that the sinus is directed away from the axis of the shell (Clathrodrillia, Calliclava, Cerodrillia, Agladrillia, Fenimorea, Decoradrillia, Leptadrillia, Syntomodrillid).
Varix can be hump-like (a wide mound—wider than tall—that projects only marginally above the circumference of the penultimate whorl when viewed apically), positioned about'/»- to V3-turn from the edge of the outer lip (Clathrodrillia, Calliclava, Fenimorea, Neodrillia, and Splendrillia), or /4-turn from the edge of the outer lip (Agladrillia). If not hump-like, it is usually narrower and taller (projecting above circumference of the penultimate whorl), and positioned ¼ to 1/3-turn from the edge of the outer lip (Decoradrillia, Leptadrillia, Lissodrillia, Syntomodrillid), or cup-handle-like positioned 1/2-turn from the outer lip (Cerodrillid), or merely an expanded rib, almost always the last (Bellaspira). The cup-handle varix is somewhat like the name implies but differs in having a slight hollow (on its trailing edge), not a hole for one's finger.
Surface microsculpture is minute sculptural elements present on the teleoconch shell surface, visible under a dissecting microscope at 10-70x magnification. In limited instances, higher magnification SEM images are used to illustrate generic difference in microsculpture. The dissecting microscope may reveal spiral grooves, lines, or ridges, fine to coarse spiral threads and fine to coarse growth striae. Ridges are formed when one side of a groove is higher than its opposite side. Spiral grooves (or ridges) and growth striae form "pits" between growth striae, aligned by the spiral grooves, have been described as shingle-like or "butterfly wing scales-like" by some authors. This pattern is found in all Fenimorea. Jagged or wavy fine spiral threads that are more numerous, finer, and more closely packed without the formation of pits are seen in Decoradrillia; incised spiral lines only (Bellaspira, Splendrillia); deep spiral grooves forming spiral bands, cords or threads that may be at times combined with grooves or ridges (Agladrillia, Clathrodrillia, Calliclava); of raised, closely-packed spiral threads made coarse by intersection of growth increments (Neodrillia), fine threads to distinct ridges confined to shell base or just the anterior fasciole, the rest of the shell mostly smooth or waxy in appearance (Cerodrillia, Leptadrillia) or glossy with microscopic threads or grooves between the ribs (Syntomodrillid) or spiral microsculpture altogether absent (Lissodrillid). The distinctly different patterns of microsculpture differentiate genera.
Anterior canal is either short (Bellaspira, Cerodrillia, Fenimorea, Lissodrillia, Neodrillia, and Splendrillia), moderately long (Agladrillia, Calliclava, Clathrodrillia, Syntomodrillia, and Decoradrillia), or long (Leptadrillia). Short usually means that there is no inflection or bend in the edge of the outer lip near the anterior end of the canal. The anterior fasciole is the dorsal, or external, side of the canal.

Diagnosis. Shell small to medium-sized, more or less claviform with an elevated spire and short base, siphonal canal short; anal sinus on shoulder slope, shallow to deep, often constricted by a parietal pad, usually with a stromboid notch; often a varix on last 0.6 whorl. Protoconch usually domed or papilliform, of ca 1.5-3.5 whorls, usually smooth, sometimes with a median keel, sometimes with preterminal axial riblets. Operculum with a terminal nucleus.
Radula. Subradular membrane strong, five teeth per row. Central tooth small (sometimes absent), with a median cusp and often with side denticles. Lateral teeth more or less wide, arched and pectinate. Marginal teeth varying from flattened scalpel-like plates, sometimes with a weak accessory limb, to hollow, enrolled hypodermic teeth (Bouchet et al 2011).

Common features of Drilliidae:
1. A fusiform shell, truncated anteriorly in most genera, usually glossy, with a tall spire, and a large last whorl usually 50% or more of the total shell length;
2. Smooth protoconch of 1,5-3 whorls. A median carina present in some;
3. Sculpture primarily of axial ribs; some genera with spiral grooves, incised lines, or threads that may be between or override ribs; subsutural cord absent;
4. Surface microsculpture of spiral grooves or threads present on at least part of the shell surface in all but a single genus (Lissodrillia); incremental growth lines can be absent, microscopic or strong;
5. Anal sinus on whorl shoulder adjacent to suture, shallow to moderately deep, usually U-shaped;
6. Parietal callus or lobe at the posterior end of the aperture beside the anal sinus; and
7. Varix present in fully developed individuals.