86 



half of tlie shell, but towards the apex the section is circular. Township 

 of Grimsby ; Niagara formation. J. Pettit. 



Genus Oncoceras. Hall. 

 This genus and Cyrtoceras pass gradually into each other, but may be 

 retained with benefit to science for those species which are much inflated 

 in the anterior half or two-thirds of the length. Of these there are many 

 species which form a peculiar and interesting section. 



Fig. 25. Fig. 26. 



Fig. 25. — Oncoceras Teucer. 



Fig. 26. — " Pettiti, A small specimen. 



0. Teucer, n. sp. — Shell much constricted near the aperture ; strongly 

 tumid on the ventral side ; gently concave on the dorsal aspect ; becom- 

 ing more slender towards the apex. Section with the dorso-ventral diameter 

 a little less than the lateral. Length of the specimen following the outer 

 curve 23 lines ; in a straight line 20 lines ; transverse width in the con- 

 striction near the aperture 7 lines ; at the most ventricose part, appar- 

 ently at the third septum 8 lines ; dorso-ventral diameter at the constric- 

 tion 6J lines ; at the third septum 8 lines ; depth of chamber of habitation 

 about 4 lines. The three last septa appear to be about 1 line distant 

 from each other in the middle of the ventral side, but as they are obscurely 

 seen, further proof is required. Siphuncle unknown. Surface with obscure 

 engirdling striae or minute folds of growth. Township of Grimsby : Nia- 

 gara formation. J. Pettit. 



0. Pettiti, n. sp. — This species attains a length of four or five inches, 

 and is somewhat variable in shape, the smaller individuals being more 

 rounded in the section, and slightly more curved in the apical half. They 

 all have the form peculiar to the genus, — constricted at the aperture, gra- 

 dually enlarging for one-third or one-half the length, and then tapering 



