Diagnosis. According to Bartsch (1943: 83-84), broadly conic shell, protoconch 2,5 whorls, the last with closely spaced hair-like axial threads, teleoconch with strong axial ribs, weak in the anal sinus, evanescent on the shell base. Ribs are overridden by axial striae and crossed by strong spiral threads, about the same distance apart as their interspaces, imparting a screen-like texture to the shell surface. The anterior fasciole has stronger spiral than axial threads. The outer lip has a weak stromboid notch and a strongly channeled anal notch; the anterior canal strongly channeled. A heavy varix lies about 1/3-turn behind the edge of the outer lip. The inner lip is appressed to the columella and forms a knob on the parietal wall at the junction with the outer lip.
Key characteristics. The combined presence of all the following characteristics is diagnostic of Neodrillia and separates the genus from other TWA drilliid genera:
1. Shell surface microsculpture of raised spiral threads, spaced two or more times their width, made coarse by microscopic growth striae.
2. Anal sinus deep, slightly constricted at its entrance, and offset from the shell's axis by the parietal lobe and outward curve of outer lip, such that it appears spout-like;
3. Ribs narrow to broad, run from suture-to-suture on spire whorls, reduced in the sulcus in later whorls, and evanescent on shell base; and
4. Varix heavy, wider and higher than adjacent ribs, positioned about 1/8-1/3-turn from the edge of the outer lip. Because Neodrillia is a relatively small genus, generalizations are necessarily tentative. Species fall into two
separate and distinctly different morphological "types" that are linked to their habitat (although expressed differently) as is possibly the case in Fenimorea. The shallow water species, Neodrillia cydia Bartsch, 1943, has a shorter spire and broad ribs, while the deep water species (>50 m), such as Neodrillia princeps, new species, have tall spires and narrow ribs.
Similar genera. Fenimorea and Clathrodrillia are similar in some respects to Neodrillia. Fenimorea has a different microsculpture; spiral threads are much finer, sub-equal to growth striae. The shell surface appears and feels smooth, and may be glossy in species with even finer microsculpture, not dull with a sandpaper-like feel as in Neodrillia. Clathrodrillia also has a different shell microsculpture. It consists of spiral incised grooves that may be close, creating the appearance of heavy spiral threads, or of overlapping bands when further apart. Whorls are usually turreted in Clathrodrillia, but not so in Neodrillia.
Distribution. Neodrillia cydia is the most abundant member of the genus and distributed throughout the TWA, although rarely appearing in the Gulf of Mexico. It is a very successful component of the molluscan shallow reefal communities and the most widespread of the Drilliidae in the TWA region. Its congeners, which inhabit deeper water (mostly >100 m), have so far been taken from more restricted ranges.

Shell comparatively small, white, rather broadly conic with a sharp apex. Nuclear whorls 2.5, the first 1.5 smooth, succeeded by a part that has very closely spaced hairlike axial threads, and this is succeeded by a part in which the axial sculpture consists of slender riblets which are distantly spaced, which in turn passes over to a portion having axial ribs plus weak spiral striations, an acceleration of the adolescent sculpture. The postnuclear whorls are marked by strong, somewhat knoblike axial ribs which extend feebly over the sinus at the summit and evanesce on the base, and numerous, very fine axial threads. The spiral sculpture consists of rather strong threads which about equal the spaces that separate them. The fine axial threads cross the depressed grooves between the spiral threads and give to these a fenestrated appearance, that is, a somwhat clothlike or screenlike texture, which is also present on the base. The columella is marked by spiral and axial threads, the first being stronger than those on base and spire, increasing in strength toward the tip. Aperture moderately large, strongly channeled anteriorly and posteriorly with a feeble stromboid notch. The portion between this notch and posterior sinus is protracted into a claw-like element. There is a heavy varix about one-third of a turn behind the edge of the outer lip. The inner lip is reflected over the columella as a heavy callus which extends over the parietal wall and forms a knob at its junction with the outer lip. Genotype: Neodrillia cydia, n. sp.
This genus differs from Drillia proper in not having smooth nuclear whorls and in not being umbilicated, and in being much more slender. It also resembles Viridrillia, but differs from it in having an entirely different nuclear scupture. In Viridrillia the axial riblets extend almost to the very tip of the nucleus, while in this group the early whorls are smooth.