XEPTUNEA VENTRICOSA. 171 



predominant dextral forms of the various zones of that formation, tlie typical N. 

 (iiifif]na being exceeding-ly rare. At the Icenian stage N. confraria liad well-nigh 

 disappeared ; N. dcxpcfta occurs there, but not very abundantly, while N. antu/v(i, 

 var. striata, becomes one of its characteristic fossils. The typical Recent and finely 

 striated form of N. antiqna. is a Pleistocene rather than a Pliocene shell. 



The fossil evidence shows, however, that in Crag times these two dextral groups 

 were closely allied. We find occasionally specimens as to which it is not easy to 

 decide whether they are a despccta-Wke variety of N. anthjua, or an <uiti(]va-\\\<.e 

 variety of N. despecta ; the one represented in PL XVII, fig. 2, agrees with the 

 latter in form, but has fine spiral sculpture; on the other hand Ave occasionally 

 meet with shells having the strong ribs of N. despeda with a somewhat more 

 elongate spire. 



The history of these shells may illustrate the origin, distribution and local 

 extinction of species. Such specimens as that of N. despecta var. intermedia with 

 dei<pecta-\\ke form and a}iti<pia-\\V^e sculpture, may have been gradually modified in 

 the direction of the finely striated N. antiqun of British seas, while the coarsely 

 ribbed varieties, no longer known as British shells, have survived on the coasts of 

 Massachusetts as N. decemcostata, in the North Pacific as N. intersculpta, or in 

 Scandinavian and circum polar regions as different varieties of ^Y. despecta. 



There must have been a time in the history of mollusca which originated as 

 varieties when, intermediate forms having disappeared, they became entitled 

 to specific rank. AVhatever may have been the case originally, however, it seems 

 to me that these two groups are at present distinct, and that it is desirable to 

 retain the nomenclature so long and so geiierally adopted, especially in view of the 

 fact that at present the one is British and Scandinavian, the other Scandinavian 

 and Arctic. 



Neptunea ventricosa (Gray). Plate XXIII, fig. 20. 



1839. Ftisus veritricosus, Grray, Zool. Beech. Voy., p. 117. 



1841-70. Fustcs ventricosus, Gould, Rep. luv. Mass., ed. 1, p. 285, fig. 200, 1841; ed. 2, p. 373, 



fig. 640, 1870. 

 1843. Fusus ventricosus, De Kay, Nat. Hist. New York, p. 144, pi. viii, fig. 183. 

 1872. Trophon ventricostis, S. V. Wood, Mou. Crag Moll., 1st Suppl., p. 22, tab. iii, fig. 4. 



1880. Fusus ventricosiis, G. B. Sowerby, Thes. Concli., vol. iv (Fusus), p. 93, pi. ix, fig. 98. 



1881. Neptunea (Sipho) ventricosa, Kobelt, Martini uud Chemnitz, Conch. Cab., ed. 2, vol. iii 

 (Purpuracese), p. 78, vol. xxv, fig. 6. 



Specific Characters. — Shell ovate, rather thin ; whorls convex, rapidly tapering, 

 the last ventricose, much the largest, forming four-fifths of the total length ; 

 ornamented by fine, rather irregular spiral ridges, with spaces between them of 



