The original description of the genus was very brief: "for the generally brown or brownish clathrate species a few of which are found in nearly every fauna, and of which Pleurotoma gibbosa Reeve may be specified as a typical example..." (Dall, 1918: 317). Not long afterwards, in his seminal work on the gastropods of the Bowden Formation of Jamaica (Miocene), Woodring based his diagnosis of Clathrodrillia on an illustration of Clathrodrillia gibbosa (Born, 1778) in Kiener (1840: pi. 16, fig. 2), and so was naturally limited by having only a single example of the genus, which he stated "seems to be a valid genus" (Woodring, 1928: 152). His description included two characteristics, a short, wide aperture and toothed outer lip that are true of C. gibbosa but not of all species included in the genus today. Subsequent workers emphasized one or more characteristics of the genus but did not specify all those that set Clathrodrillia apart from other genera in Drilliidae, e.g.: "The hump-backed variced body whorl is considered diagnostic of this genus." (Powell, 1966: 73). Some species in the genera Fenimorea, Splendrillia, Neodrillia, and Calliclava also possess this type of varix. Or: "Its wider, shorter aperture than in Crassispira and particularly the definite stromboid notch and shallow spiral furrow of some width leading to the notch set it apart" (Fargo, 1953: 368), who seemed to have followed Woodring's description, but a clear mischaracterization of Clathrodrillia, which has a longer narrower aperture than Crassispira. Neither the form of the varix nor of the aperture alone is sufficient to separate Clathrodrillia from other genera in Drilliidae. Olsson (1964: 95-96) gave a broader diagnosis of Drillinae [sic], based on the model of C. gibbosa, and included such disparate genera as Hindsiclava and Compsodrillia. This accommodation required the diagnosis to include a "ridge-like spiral cord at the suture", a feature not present in the family as it is known today.
The following diagnosis is a more complete diagnosis of the genus. Shell small to large (13-60 mm), slender with a high, acutely pointed spire composed of flat to convex whorls having a concave anal sulcus below the suture. Aperture narrowly oval, only slightly wider at its widest than the anal sinus and canal at opposite ends. Anterior canal well demarcated and of short to moderate length, and a weak to strong anterior fasciole with or without a weak false umbilicus, or chink. Protoconch of 2-3 smooth whorls. Sculpture of numerous ridged axial ribs (crests narrow, not round) that extend from suture-to-suture but are greatly reduced and recurved in the sulcus giving the shell a shouldered or turreted outline in most species; ribs either straight or slightly opisthocline. Varix hump-like in most, positioned ¼ to 1/3-turn from the outer lip. Strong spiral sculpture of incised grooves that create the appearance of bands, cords or threads that override or cut the axials. Outer lip thin, flattened from varix to lip edge, strengthened by irregular axial folds, with a stromboid notch anteriorly, and anal sinus posteriorly; edge of lip may be scalloped or "toothed" by spirals, or not. Inner lip margined, recumbent or erect, usually relatively wide; with a callus on the parietal wall at the anal sinus. Anal sinus deep, U-shaped, adjacent to the suture, offset from shell axis by parietal lobe and projected laterally so that it appears spout-like.
Key characteristics. The presence of the following characteristics is diagnostic of Clathrodrillia and separates the genus from all others in Drilliidae:
1. Strong spiral sculpture of grooves or cords; grooves may create the appearance of cords when close together, or broader bands when further apart;
2. Axial ribs that extend from suture-to-suture, and to the anterior fasciole on the last whorl; reduced in the sulcus;
3. Aperture narrow, only slightly wider than anal sinus and anterior canal; and
4. Varix hump-like (low and broad, shallow water species), or narrow and high (deep water species), positioned about 1/4- to 1/3-turn from the edge of the outer lip, usually with a dark color patch.