Hyatt.] 300 [April 4, 



also resemble the genus Discitoceras in general aspect during 

 the later adolescent and adult stages. 



Nephriticeras, 1 nobis, includes Devonian forms with ellipti- 

 cal or broad kidney-shaped whorls. There is an impressed zone on 

 the dorsum at a late stage in the elliptical forms, and in the kid- 

 ney-shaped whorls this appears at earlier stages. The umbilical 

 perforations are large, and the whorls arcuate until a compara- 

 tively late stage of growth in all except the highest smooth forms. 

 Siphon is nummuloidal, and near, but above the centre. The 

 sutures have broad ventral saddles in the adolescent usually with 

 slight ventral lobes in the adults. The lateral lobes are also slight 

 and broad, the dorsal lobes are similar, and have large V-shaped 

 annular lobes in the impressed zone, the last often being very 

 large, and cones are partially formed. The living chambers are 

 from one fourth to half a volution in length and very broad, the 

 increase of the whorl by growth being very rapid. The longitu- 

 dinal ridges in the radical species, such as Neph. (Naut.) cornu- 

 lum, sp. Hall, and their arcuate later larval stages, and adolescent 

 gyroceran forms without impressed zones, and central nummu- 

 loidal siphons and sutures lead to the conclusion, that the genus 

 sprang from some unknown ridged and probably Devonian form 

 similar to Uranoceras, and Aploceras. Type, Neph. (Naut.) buci- 

 num, sp. Hall, Nat. Hist. N. Y., Vol. 5, pt. 2, pi. 60, 109. Mus. 

 Geol. Surv. Albany. 



Cenoceras, 2 nobis, includes forms appearing in the Trias, 

 Jura, and Cretaceous, with nummuloidal siphons, flattened abdo- 

 mens, sides but slightly convex and convergent, the abdomen 

 narrower than the dorsum. The siphon is nummuloidal, and, 

 though near the centre, may be either above or below it. This 

 again in the young occupies a position on the ventral side of the 

 centre in the few forms known. The shells are nautilian from 

 an early stage with decided impressed zones in the adults. The 

 septal cone becomes in this genus separable from the sutural lobe 

 with which it was combined in Nephriticeras. The transitional 

 Triassic species, like Cen. (Naut.) carolinum, and Tintoretti sp. 

 Mojsis. Med. Trias Prov., may have either ventral saddles or lobes 

 in adults, and siphon central or below centre except in the young, 

 and whorls which are not very involute. Jurassic species, though 



i N€<|>piTqS) kidney shaped. 2 Katvos, modern. 



