﻿dall] REVIEW OF FROG-SHELLS AM) TRITONS 1 2J 



has it long ami narrow with apical nucleus; Cabestana (cutacea) 

 concentric with nucleus sub'central ; Gyrina (gigantea) ovate and 

 slightly arcuate with the nucleus apical as if making- an effort Inward 

 spirality; Fusitriton {oregonensis and cancellata) broad ovate with 

 the nucleus slightly within the anterior lateral margin ; Lampusia 

 i pileans) has it fusoid. According- to Adams the Ranellas have the 

 operculum ovate with an apical or subapical nucleus, while Gray 

 speaks of it as half ovate with a central, lateral or internal nucleus; 

 probably it varies in the different groups as in the tritons; in Ranella 

 foliata it is figured as concentric with the nucleus mid-lateral. One 

 cannot safely generalize on this character until the operculum of 

 more species is known. 



The protoconch and nepionic shell in the Tritons are practically 

 continuous and inseparable, and are apparently very similar if not 

 identical in character in both the tritonoid and ranelloid groups. In 

 one group alone, Septa, is there a distinctly marked neanic stage. 

 The nuclei of the Australian fossil forms, as figured by Kesteven, in- 

 dicate that a protoconch, as distinguished from the nepionic shell, 

 was present in some if not in all these forms : a character of much 

 interest and importance if confirmed by a renewed study of the fossils, 

 which are not accessible to me. 



I have observed the larval stage of Fusitriton oregonensis swim- 

 ming free in the ocean in the Gulf of Alaska some 200 miles off 

 shore. It had a horny shell of more than three whorls with numerous 

 spiral keels of periostracum and hardly any trace of a sulcus at the 

 base of the pillar. The operculum was broadly triangular, pointed 

 laterally, with the subspiral nucleus within the margin and forming 

 half a coil. Below the posterior edge of the operculum were two 

 short and wide epipodial lappets, separated by a sharp sulcus. The 

 head was represented by a rather high, pointed, brown papilla above 

 the mouth, and on each side of the body was a rather large epipodial 

 flap or flipper, which the larva used vigorously to propel itself 

 through the water, giving it a curious resemblance to a Pteropod. 

 The branchia and osphradium were already almost normal, but the 

 parts about the oral aperture very little developed. The flippers were 

 of a bright metallic green color, rendering the little animals very 

 conspicuous in the water. There were, as far as observed, no eyes 

 or tentacles developed, and the foot, except as a pedestal for the 

 operculum, hardly existed. The larval shell of Colubrellina cubaniana 

 D'Orbigny, from the West Indies is heliciform, with no trace of a 

 siphonal canal, at first distinctly umbilicated and ornamented with 

 numerous spiral series of minute bristle-like hairs, which are soon 



