No. 471] ANATOMY OF ACM.EA TESTUDIN A LIS 



173 



litoral animals. The first one, the AcmaM(l;i'. coinpri-cs those 

 limpets which retain the primitive ^ill fctenidiiiin ' with or with- 

 out a cordon of branchial leaflets; the second, the I'aicllida'. 

 comprises those which lack a ctenidimn hnt have a luaiicliial 

 cordon. The AcmaMda' contains three (rcncrn: l*cc(iiiodoiitii. 

 with one species, a deep-sea form found oil' some of the West 

 Indian islands; Acmsea, with ei<,dity-four species, of almost woHd- 

 wide distribution; Scurria (includiufr the subfremis Lottia), whose 

 five specues are found only on the AVest American coasts, as far 

 north as San Francisco. The Patellidie contains also three cren- 

 era: Patella (including the subgenus Ilelcion and the sections 

 Patina, Scutellastra, Ancistromesns, all often rcnanlcd a^ uvncra), 

 with forty-eight species which with one exception P. i/n.ricdna) 

 are entirely restricted to the Oh I World; Nacclla. wl,o>c >cven 

 species are found only in the region al)out the -^ontheiii part of 

 South America; Ilelcioniscus, with forty-eii;lif >[>eci<'^ in xai'ioiis 

 portions of the Indian and Pacific Oceans but not extending on 

 the American coast farther north than Chih. 



Tiic name rafrlla .Amnnn Ir.t udiualis (ir.t appear, in 1770 

 in Muller's Pmdromus but more than fifty w-ar. uent l.x before 

 any record was made of so obvious a feature in it> anatomy a- the 

 possession of a ctenidium. It was the observation of tlii> fa<-t 

 which led EschscholtJi to establish in 1.S30 the new uenus Acnia-a. 

 As is well known, his earlv death left micompleted th,. /.nuln<,,srhrr 

 Alias which was to have enil>odi<Ml the rcMilt^ accumnlated dnring 

 the years of his circumna\ igatin- voyaues. Such material a^ was 

 in ccmdition to be used by another was complete(l by his friend 

 Uathke and pid)lished in bs;i;] as a lifth part of the .l//a.v. it , ,,„- 



new genus Acma-a followed by brief descriptions, .lealing with 

 oidy the shells, of eleven specie^ collected In i^cliM hoh/ in the 

 neighborhood of Sitka. 



