382 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



3. surculites, Conrad. * 



Shell with spire and body-volution nearly equal ; the latter 

 obconical, rectangular near the top, and flattened or concave above 

 from the angle to the suture ; sinus of lip above the angle of the 

 whorls, shallow and broad. — (S. annosa, Conrad.) 



4. g-enota, H. and A. Adams (not Adanson). 



Shell mitriform ; canal rather short; surface cancellate; outer 

 lip with a deep posterior sinus. — (T. mitriformis, Wood.) 



H. and A. Adams, in their valuable work on the genera of recent 

 Mbllusca, include two other sections of recent species in tins genus, under 

 the names Brachytoma, Swainson, and Conopleura, Hinds. The former of 

 these groups is represented by Pleurotoma strombiformis, Sowerby, which 

 has its outer lip thickened, ascendin'g, and forming a short canal, and its 

 inner lip thickened above ; and the latter, by C. striata. Hinds, a short shell, 

 with a depressed spire, a very short canal, and a deep sinus in its outer lip 

 near the suture. I am not well acquainted with these shells, but, judging 

 from the published figures, would suppose they might better be separated 

 entirely from this genus. 



A thorough revision of all the known fossil and' recent species that have 

 been described under the name Pleurotoma, would doubtless show good 

 reasons for separating subgenerically, or, in some cases, generically, several 

 other types, and probably for including as subgenera a few that have already 

 been separated as genera. Not having at hand, however, the necessary 

 materials for such a revision, no attempt of this kind is made here. 



The shells of this genus resemble more or less nearly those of the genera 

 Drillia, Beta, Lachesis, Clavatula, Perrona, Clathurella, &c, many of which 

 were formerly, along with those of some allied groups, "often referred to this 

 genus under the name Pleurotoma. They are all distinguished, however, by 

 various characters, such as the inrlexed outer lip, thickened inner lip, and 

 shorter recurved canal of Drillia; the flattened columella and shorter canal 

 of Bela; the mammllate apex and slightly thickened and internally crenate 

 outer lip of Lachesis; the operculum with its nucleus at the center of the 

 straight front edge in Clavatula and Perrona; and the entire absence of an 



* I believe Mr. Conrad never characterized his proposed subgenus Surculites ; but his type-species 

 has the characters given above. It seems to he very near Surcula, but may probably be retaiued for a 

 group of Tertiary species, with obconic body-volutious, usually referred to Pleurotoma, and forming a 

 kind of transition from Pleurotoma toward the Couidw. 



