﻿MOLLUSCA.-HEDLEY. 



105 



iis a convenience it would be desirable to break up a genus so 

 vjnwieldy as Rissoa is according to Tryon's presentation. 

 Bearing in mind that the type of Rissoa, Freminville, 1814, is 

 Turbo cimex., Linn.,l it is clear that many of the Australian 

 shells usually so called are not entitled to the name. 



In studying the Rissoidae taken by the "Thetis" Expedition, 2 

 I noted that, though Watson's subgenus Scrobs had been 

 reduced by Tryon to a synonym of the earlier .1 nipliithalamus, 

 Carpenter, yet Carpenter's type was rejected by Tryon as 

 insufficiently known. Under these circumstances it seemed 

 unsafe to use Amphithalamus. 



By the kindness of Mrs. B. Williamson, of Los Angeles, Cali- 

 fornia, I have received a specimen of the type species of the 

 genus .4. inclusus, Carp., collected by Jvlr. Henry Hemphill. 

 No illustration of the species seems to have yet appeared, so 

 I figure (PI. XX., fig. 34) the gift of Mrs. Williamson, which 

 had been identified as .1. inchisus, Carp.,3 by Dr. W. H. 

 Dall. On this foundation I can now accept and use Tryon's 

 interpretation of the synonomy. .A paper on the \\'est Ameri- 

 can members of Amphithalamus, which Dr. P. Bartsch has 

 published this year, has not yet reached me. 



The American shell at once recalls A. jacksoni, Brazier, to 

 a less extent .4. petterdi, Brazier, and .4. scrobiculator, 

 Watson. Besides these three small species with detached 

 aperture there are others tightly coiled which vary from broad 

 and short to tall and slender. As uncoiling is considered a 

 degenerate feature, the larger, longer, more tighth' wound, 

 many whorled, elongate, fusiform shell is probably nearer 

 to the ancestral form of the genus. 



Hab. — Numerous specimens from 100 fathoms fortv miles 

 south of Cape Wiles, South Australia. 



It has frequently happened that the Australian species of 

 this group have been described under one name in one serial 

 and figured under another name in another publication. Under 

 these circumstances it seems useful to indicate what species 

 might be referred to Amphithalamus. I would suggest the 

 following : — 



A. APPROXiMUS, Pettenl. 



Rissoa approxima, Petterd, Journ. of Conch., iv., 1884, p. 

 138; id., Tate and May, Proc. Linn. Soc. N.S. W'ales, 

 xxvi., 1901, pi. xxvi., f. 69. 



1 Herrmannsen— Ind. Gen. Malacol., ii., 1849, p. 400. 



2 Hedley— Mem. Austr. Mus., iv., 1903, p. 353. 



3 Carpenter— Ann. Mag. Nat. Hist., xv., 1865, p. 181. 



