FIFTH, OK v. VSSK I'.KAN i:i: VN< II. 





quadragonatum, Htatt. 



A form in the Museum of Comparative Zoology, represented in Figures 84, 



35, closely resembles the Btout variety of obtusion, but exaggerates the char- 



of thai form and <>i variety 1>. Though young, it bas a more Bubquad- 



kl whorl than is usual in the adults of obtusion, var B, i flatter abdomen 



and broader channels, and quite distinct piliB, with a tendency to the formation 



of tubercul hub, though actual tubercles are not present. The diameter 



mm. The outer whorl is *Jn mm. <>n the sides, and the transverse diameter 



me. The about parallel, the abdomen flat, distinct, Bub-angular, 



and genicular are present. The abdominal part <»i the pilaa do not bend forward, 



but pass "ii t<> the abdomen and interrupt the channel ridges. The ridges are 



well marked, though not bo prominent as in I 



I- - • . lently a modified form <>! obtusum, in which the pilaa by a very slight 



ilae would become tuberculated. Dumortier, in liis M fitudes 



Pal. Bassin «lu Rhone," describes a specimen of obtusum having eight or nine 



; p< hi the young w borls until *J<» mm. in diameter, and gives tl 



of the young of hi* specimens, Thej probably belonged to this 



i the young are more strongly marked in this waj than is usual 



in other varietii 



Thei ecimen in the Museum of Comparative Zoology, from Lyme 



">00 mm. in diameter. Though considerably altered by pressure, the last 



whorl lias the a* xdragonatum, and the normal form is comparatively 



slightly altered on the third qnarter of this volution. It i- here onlj 115 nun. in 



abdomino-dorsal diameter, which is considerably less than would occur in any 



equally large specimen <>f other varieties. 1 n the 



outer whorl, but these may in large part be dui of the p. 



m»T I* «im|>lv a ra*. o( ptrmlb - 



