276 AMERICAN JOURNAL 



small close to anal, aperture minute ; anal do., larger, furnished 

 with papillae inside the orifice ; infra-anal do., smaller at the 

 extreme right. Ejes small, on external base of tentacles. A 

 puckered frill exists on the sides of the foot, extending all 

 around except under the head. Formula, — - — " , „ ^ 



Lives on floating fuci near Cape Horn. 



This remarkable species was early known to naturalists, 

 although its range appears to be comparative!}'' limited ; as far 

 as we know, it is confined to the shores of Tierra del Fuego and 

 the Straits of Magellan, where it finds a congenial home among 

 the giant sea weeds for which that coast is noted. It is the ana- 

 logue of Patina pellucida of Britain, but the arrangement of 

 the teeth and branchiae being quite different, they cannot even 

 be placed in one genus. 



This species, described by Gmelin under the name of Patella 

 mytilma in one part of the Syst. Nat., is further on described 

 again under the name of P. conchacea, with the identical refer- 

 ences to Martini's paper which he had used in the first instance. 

 Lamarck afterward gave it the name of cymbularia, by which it 

 is best known ; while Schumacher's name, mytiloides, though 

 given before that of Lamarck, has been frequently quoted as a 

 synonym of the latter. The references given by Gmelin are all 

 to non-binomial authors, and the ' name mytilina, having ten 

 pages precedence of conchacea, has been here adopted. I have 

 been unable to discover the name cymhuloides in D'Orbigny's 

 work, which Gould quotes as a synonym. No other species is 

 at present known, and the forms from the west coast of North 

 America which have been called '■'•Nacella' will be distributed in 

 difi'erent groups, but probably most of them will find a place in 

 Colluella. 



The colors are from Couthouy's notes, taken from the living 

 animal, the anatomical details from specimens collected by him. 



Genus HELCION, Montfort. 



Helcion^ Montf., Conch. Syst. 1810, ii, p. 62. Blainv., Malac. 



1825, p. 499. H. and A. Ad., Gen. Rec. Moll, i, p. 460, 



ii, p. 657, 1854. Gray, Guide, p. 176. P. Z. S. 1847, 



p. 168. Cpr., Lect. Second. Ed. p. 72. 

 < ITelcion, Chenu, Man. de Conchyl. i, p. 375. (?) Meek, Check 



List Cret. Inv. U. S. p. 17, 1864. 

 Patelloidea sp., Cantraine, Bull. Ac. Sci. Brux. 1835. 

 Helcium, Meek and Hayden, Am. Journ. Sci. and Arts, vol. 



xxix, second series, p. 83 (? err. typog.) 



