Hyatt.] 292 [April 4, 



similar in form to the larva of Trem. subsulcatum, and later take on 

 the ridges and abdomen as in Strob. Hartii, but develop a broad 

 furrow between the two ventral ridges. This furrow with the two 

 lateral furrows form a trisulcated abdomen, and together with the 

 ventral lobes in the sutures enable us to separate the species from 

 the adults of Strob. Hartii. The siphon is near the venter 

 The small dorsal lobe is first formed in the centre of the dorsal 

 saddle, simple as in Stroboceras. Then a minute saddle arises 

 dividing it into two V-shaped lobes. This genus also includes 

 species with young more evidently similar to the adults of Tri- 

 gonoceras, as is shown in Gaudry's figure of Trem. (Naut.) sub- 

 sulcatum, Ench. du Monde Anim. Foss. Prim. p. 174, but which 

 speedily in course of growth elevate the abdomen and develop 

 ridges. In successive stages the ridges disappear, and the abdo- 

 men and sides become flattened, forming a whorl which in section 

 is typically tetragonal and similar to Discitoceras. The siphon is 

 near the venter in the young, and shifts to midway between 

 the centre and the venter in the full grown. 



Discitoceras, nobis, is equivalent to the genus Discites, 

 McCoy, Synop. Carb. Foss. Ireland, p. 17. It includes species with 

 quadragonal whorls having the abdomen slightly convex, sides 

 flattened, the dorsum very gibbous. There is also a slight 

 impressed, dorsal zone. The young are ridged longitudinally 

 with prominent transverse striae, but though these cross and 

 roughen the ridges, they do not render them subspinous. The 

 sutures have ventral, and lateral lobes, aud broad dorsal saddles 

 with small annular lobes. The siphon is above the centre. The 

 living chambers vary from one-fourth to three-fourths of a volu- 

 tion in length. The aperture has a very deep ventral sinus, with 

 large lateral saddles near the dorsum, and small lateral sinuses 

 The type, Dis. costellatum, McCoy, Op. Cit. pi. 2, fig. 4, was appar- 

 ently the young of a species similar to his Dis. discors. The name 

 Discites has been used by DeHaan, Walch and Schlotheim for 

 genera of Mollusca, and we, therefore, substitute another name 

 for that first announced by McCoy. 



Phacoceras, 1 nobis, has whorls compressed and acute in the 

 adults, but with young similar to the adults of Discitoceras. The 



•*oLkos, a lentil. 



