CRETACEOUS FOSSILS. 453 



Surface of the shell marked by strong-, distant, transverse, encircling- 

 ridges, which are directed slig-htly forward in passing from the dorsal to 

 the ventral margin, and in crossing the latter they become nearly obsolete. 

 Occasional intercalated ridges occur at irregular distances on the dorsal 

 side. Intercostal spaces concave. The shell is further ornamented by two 

 lines of obtusely-rounded nodes, which are situated on the ribs at the 

 angles of the flattened dorsum. 



Septa somewhat complicated and closely arranged, so that the inner 

 lobes interfere with the extremities of the sinuses of the preceding ones, but 

 on the dorsal portion they are more distant. Siphonal lobe longer than wide, 

 deeply divided at the extremity, and terminating in two large, strongly-ser- 

 rated digitations, having one or two lateral spurs on their outer sides. First 

 lateral lobe large, deeply bipartite, each branch terminating in two or three 

 unequal digitations, and with several smaller spurs on the sides above. 

 Second lateral lobe much smaller than the first, deeply bipartite, with 

 numerous strong spurs irregularly arranged along the margins. Anti- 

 siphonal lobe long, narrow, and simple, but with long lateral serrated spurs 

 and a slightly tripartite extremity. First and second sinuosities rather 

 large, deeply divided by large auxiliary lobes into two principal branches, 

 which are again deeply divided. Third sinus smaller than the others, and 

 divided into two principal branches. The margins of all lobes and sinuses 

 deeply serrated. 



The species is described from an imperfect individual and a second 

 smaller fragment of a larger specimen. They consist only of the convolute 

 parts, and show no evidence of the deflection of the tube. It is possible 

 they are not rightly referred to the genus Ancyloceras, but are more nearly 

 related to the genus Anisoceras of Pectet, which differs from the former 

 genus in being irregularly helicoid. The example figured of Plate 16, 

 Figs. 7-9, would seem to have been somewhat irregularly coiled, but this 

 may possibly be the effect of distortion, as the smaller coils of the shell 

 are considerably displaced. It differs from Ancyloceras also, as defined by 

 Mr. F. B. Meek (Paleontology of the United States Geological Survey of the 

 Territories, p. 409), in having the terminations of the lobes bipartite instead 



