PLEUROTOMIIXffi. 155 



of the lingual dentition ; conchologically the species belong in 

 Fusus. 



Genus ANCISTROSYRINX,Dall, 1881. 



Whorls concave below the suture ; with a wide deep sinus, 

 bordered externally by an elevated frill directed backwards. 

 Operculum and dentition not described. Only a single species 

 known, and its systematic position very uncertain. 



Genus DRILLIA, Gray, 1838. 



Shell turriculated, with longitudinal ribs, and usually revolving 

 striae ; last whorl usually short ; spire elevated ; columella with a 

 posterior callus ; outer lip thick, but not varicose, nor dentate 

 within, flexuous, with a well-marked posterior sinus near (but not 

 reaching) the suture, and an anterior constriction or sinuosity ; 

 canal short, curved, usually narrow. 



Principally distinguished from Pleurotoma by the smaller size 

 and short recurved canal. 



Animal with tentacles approaching at their bases and eyes 

 near their extremities. 



Distr. Warm Seas. Fossil, cretaceous, U. S.; miocene, Eur. 

 The following, generally regarded as subgenera, will be treated 

 as sections in this work : 



Section CRASSISPIRA, Swainson, 1840. Shell somewhat clavi- 

 form, tuberculated ; anterior canal very short ; inner lip with a 

 thick posterior callus ; outer lip thick within. 



Section CONOPLEURA, Hinds, 1844. Shell coniform; aperture 

 narrow, sinuous ; columellar lip callous , canal very short ; outer 

 lip sinuous, with a profound lateral sinus. 



Section CLAVUS, Montfort, 1810. Tuberculated or spiny; 

 aperture rather large ; outer lip produced below the sinus. 



Section BRACHYTOMA, Swainson, 1840. Shell strombiform ; 

 columellar lip rather thick ; outer lip ascending and forming a 

 canal-like sinus near the suture. 



Genus SPIROTROPIS, Sars., 1878. 



Shell turriculated, rather thin ; apex obtuse ; whorls carinated, 

 sinus profound, distant from the suture. Operculum normal. 

 Dentition (PI. 33, fig. 53) very distinct ; formula 1-1-1-1-1. 



