POTERIOCERAS. 113 



pJioceras by Woodward/ and Zittel.^ Barrande divided it between Gyrtoceras and 

 Gomphoceras. Foord, however, following Hyatt, not only reconstituted the 

 genus but treated it as a distinct family. 



It seems to me that the three species described below may be placed in this 

 genus without hesitation. 



1. PoTBEiooBRAS VAsiPORMB, WMdbome. PI. VII, figs. 5, 5 a, 5 b. 



1889. Gomphoceras vasifoeme, Whidhorne. Geol. Mag., dec. 3, vol. vi, p. 29. 



Description. — Shell almost straight, pyriform, tapering quickly, rather large. 

 Ventral outline slightly convex. Dorsal outline convex on the body-chamber, 

 slightly concave near the apex. Lateral outlines oblique and nearly straight. Septa 

 close, very slightly concave, rather oblique ; ratio of septal height to width 1:8. 

 Section elliptic, more or less flattened ventrally, the ventro-dorsal being to the lateral 

 diameter in the ratio of 12 : 15. Siphuncle rather large, close to ventral margin, 

 elliptic, apparently beaded in each chamber. Shell-structure not very thin ; 

 surface showing no sign of ornament. 



Size. — The best specimen I know, though defective at both ends, measures 

 47 mm. in length, and 32 mm. in ventro-dorsal, and 36 mm. in lateral diameter. 



Locality. — Wolborough. There is a good specimen in the Torquay Museum, 

 and three much poorer examples in the Museum of Practical Geology. 



BemarJcs. — This species is distinguished by its rapidly tapering, nearly straight 

 pyriform shape, and by its siphuncle being upon the shorter axis of its section. The 

 specimen in the Torquay Museum is the only one that gives the characters well ; the 

 two smaller specimens in the Museum of Practical Geology seem to agree with it 

 but are mere fragments ; the larger one appears more flattened on the ventral side, 

 and probably belongs rather to Poterioceras ellipsoideum than to this species, but 

 its state of preservation is so bad that very little can be learned from it. 



Affinities. — Orthoceratites suhfmiformis, Mimst.,^ and 0. suhpyriformis, Miinst.,^ 

 both seem to be much more elongate forms with less swollen outlines. 



Poterioceras Marri differs from it in its broader septa, its more elongate form, 

 and its longitudinal markings, and Poterioceras ellipsoideum, Phillips, sp., in its more 

 fusiform shape, its greater obliquity, its broader septa, and its less rapid dilatation. 



1 1872, Woodward, ' Man. Mollusca,' ed. 2, p. 193. 



2 1881—1885, Zittel, ' Handb. Pal.,' pt. 1, Band 2, p. 370. 

 ^ 1840, Miiust., ' Beitr.,' pt. 3, p. 103, pi. xx, figs. 6—9. 



* Ibid., p. 103, pi. XX, fig. 10. 



