MOLLUSC A OF PORTO RICO. 
385 
cancellated by spiral threads and growth lines; carina on last whorl with about twenty-six sharp 
sawtooth-like spines curved upward; halfway between this crown and the suture is a second smooth, 
sharp keel, and within is a deep sinus; aperture narrow, elongate. 
Length, 18; diameter, 8 mm. 
Mayaguez Harbor, Porte* Rico, one young specimen. 
Genus DRILLIA Gray, 1838. 
Shell turriculated, with elevated spire, the last whorl generally shorter than the rest of the 
shell: outer lip thickened; sinus rather deep, rounded, placed a short distance below the suture. 
Operculum as in Pleurotoma. 
. Drillia ostrearum Stearns. 
Drillia ostrearum Stearns, Proc. Bost. Soc. Nat. Hist., xv, p.22, 1872; Tryon, Man., vi, p. 197, pi. xxxiv, fig. 79, 1884. 
Shell with about ten whorls, which are rather narrowly eoncavely shouldered above, with 
straight, strong, longitudinal ribs (about eighteen on the last whorl), which are crossed by numerous 
revolving threads of two sizes. On the last whorl, just behind the outer lip, there is a strong varix, 
which is continued upward to the suture; aperture moderately short; canal truncated below. Color 
varying from yellow to blackish. 
Length, 18; diameter, 6.5 mm. 
St. Thomas, one yellow-colored specimen. 
Drillia albicoma Dali. 
Drillia albicoma Dali, Blake Report, n, p. 83, pi. x, fig. 8, 1889. 
Shell solid, slender, acute, white, with a simple, polished nucleus of a whorl and a half, followed 
by nine slightly convex whorls, which have rather strong, flexuous, longitudinal ribs that extend from 
suture to suture; spiral sculpture consisting of exceedingly fine, wavy threads; last whorl having a 
stout, high varix near aperture; aperture more than one-third the length of shell, narrowed below. 
Length, 25; diameter, 8 mm. 
Aguadilla, Porto Rico; one broken shell. 
Drillia eucosmia var. canna Dali. 
Drillia eucosmia var. canna Dali, Blake Report, ii, p. 86, 1889. 
Shell pale, with a peripheral lighter zone; whorls eight; longitudinal sculpture consisting of short, 
stout ribs, beginning at the fasciole and ending below the middle of the whorl; surface covered with 
revolving threads. 
Length, 19; diameter, 6.5 mm. 
Mayaguez, Porto Rico; one specimen of the variety canna, in bad condition. The variety is 
smaller and more slender than the type and has three peripheral spirals. 
Drillia nigrescens Gray. 
Pleurotoma nigrescens (Gray MS.) Reeve, Conch. Icon., i, pi. xxvi, fig. 235, 1845. 
Shell solid; whorls with rather a well-defined but low shoulder, above which they are excavated 
and finely reticulated. Below the suture there is a rather strong, revolving thread. Ribs numerous, 
fine and nearly straight, beginning at the shoulder and becoming fainter on the baseof the body whorl. 
Between the ribs are strong revolving line, which become stronger and sometimes nodulous on the 
base; varix low; aperture short, truncate below. Color dark purplish or blackish. 
Length, 12; diameter, 4.5 mm. 
Mayaguez Harbor, Porto Rico; Ensenada Honda, Culebra; several worn shells. 
Drillia ? actinocycla, n. sp. Plate 57, fig. 15. 
Shell minute, thin, brilliant (the type immature), with about seven convex whorls separated by 
a deep suture; the first four whorls are smooth polished, nepionic and translucent, those following with 
numerous narrow deeply concave, emphatic, axial ribs, extending from suture to suture but obsolete 
on the base of the whorl; these are crossed by numerous fine, equal, evenly distributed spiral grooves 
F. C. B. 1900—25 
