CRETACEOUS FOSSILS. 71 



cannot be certainly determined. Interspaces between the ribs 

 broadly concave. 

 Septum unknown. 



Figure, one-half natural size. 



Locality: "Vancouver Island," associated with Ammonites Newberryanus and 

 another Ammonite, species undetermined ; and a Baculite, figured on pi. 9, fig. 

 28 a, and pi. 6, fig. 28, 6. 



Closely allied, in form and ornamentation, to //. Fremontii, Marcou, Geol. N. 

 America, p. 36, pi. 1, fig. 3. It differs in the ribs continuing completely across 

 the ventral face, and in each rib carrying a node, instead of every third rib, as in 

 Marcou's species. 



HELICOCERAS, D'Orb. 



? H. VERMICULARIS, n. 8. 

 PI. 13, Fig. 19, and 19 a, b. 



SHELL small, subcompressed. Section elliptical. Curve broad, 

 regular. Surface marked by numerous small rounded ribs, regu 

 lar in size, and extending completely around the shell, being 

 slightly oblique and less distinct on the ventral side. 



Septum composed of a dorsal, ventral, and on each side two 

 lateral lobes. Dorsal lobe divided into two bifurcate branches, 

 with three rounded spurs above. Dorsal saddle wider than the 

 lobe, bifurcate, each branch being divided into two. Superior 

 lateral lobe about as long but wider than the dorsal ; the pattern 

 is the same. Lateral saddle shorter than the dorsal, and of the 

 same pattern. Inferior lateral lobe two-thirds as large as the 

 superior lateral, and more simple. Ventral saddle small, divided 

 into two unequal bifurcate branches. Ventral lobe half as long 

 as the preceding ; trifid at the extremity, and with two or three 

 teeth above on the sides. 



Figure, twice natural size. 



This species has only been found at one locality, namely, on a hill southwest of 

 Martinez, in Contra Costa County, in the lower division. It appears to be allied 

 to H. Mortonii, Hall and Meek, sp., Mem. Amer. Acad. Arts and Sciences, 2d 

 ser., voi. 5, p. 396, pi. 4, fig. 3, but differs in being much smaller, having proper- 



