1897.] NATURAL SCIENCES OF PHILADELPHIA. 467 



b" . Tube oval in section, compressed between the con- 

 vex and concave sides ; slowly tapering ; moder- 

 ately arcuate ; smooth except for very fine growth 

 lines, D. precursor. 



II. Shell contracted toward the aperture, which is smaller than the 

 largest diameter of the tube; smooth, Cadulus. 



a. Acicular, much attenuated posteriorly, the greatest diam- 

 eter or " equator " very near the aperture. 



b. Length 6-7 mm., about 8 times the greatest diam- 

 eter, C. phenax. 

 b'. Length 8-12 mm., about 12 times the greatest diam- 

 eter, C. elegantissimus. 

 a'. Slender, but not conspicuously attenuated posteriorly, the 

 greatest diameter near the aperture, where there is a small 

 depression on the ventral side, C. depressicollis. 

 a". Stout and short, the greatest diameter near the anterior 

 third of the length, gradually tapering toward each end ; 

 length about 4} times greatest diameter, C. colobus. 



Dentalium Cossmannianum n. sp. PI. X, fig. 11 ; PI. XI, figs. 10, 11. 



Shell a hexagonal prism with slightly convex faces, slender, slowly 

 tapering, moderately solid, glossy. Sculpture: there are 6 very nar- 

 row equidistant longitudinal threads, well raised and sharply de- 

 fined, the wide intervals between them flat on the smaller end of the 

 shell, but become decidedly convex toward the larger end ; circular 

 sculpture of rather strongly impressed annular growth marks at un- 

 equal intervals, sometimes close, sometimes distant. Aperture not 

 preserved in the material before us, but apparently not oblique and 

 with nearly circular peristome but slightly modified in shape by the 

 longitudinal threads. Apex not known, but evidently hexagonal. 



Length of (broken) type specimen 23 mm.; greatest diam. at 

 larger end 35, at smaller end 2'7 mm. 



The type has lost from the smaller end a considerable portion of 

 its original length and probably somewhat less from the oral extrem- 

 ity. When perfect it probably measured not far from 45 or 50 mm. 

 The portion remaining is perfectly characteristic, and unlike any 

 Tertiary or living species of this region in the filiform riblets run- 

 ning from end to end, with wide convex intervals showing no inter- 

 mediate longitudinal sculpture, or only the faintest traces of riblets 

 in places, visible only under the lens at a certain angle of reflection. 

 This is the form mentioned by Gabb under his remark on D. dis- 



