266 AMERICAN JOURNAL 



side and three uncini. Rhachidian tooth rarely present. Muz- 

 zle without a frill. 



Genus ANCISTROMESUS,* Dall. 

 Patella sp., Auct. 



Animal with a complete branchial cordon, the lamelh^ long 

 and slender, subequal ; sides of foot smooth ; radula furnished 

 with a simple rhachidian tooth ; the two inner laterals on each 

 side anterior to the third pair, which are large and quadriden- 

 tate. Uncini simple. Shell very large in the adult. 



Type Ancistromesus mexicanus, Dall ex Brod. PI. 15, fig. 21. 



Patella mexicana, Brod. and Sby., Zool. Journ. vol. iv, p. 

 369. Bve., Conch. Icon. Patella, pi. i, f. 1. 



Animal generally blackish, more or less marbled and streaked 

 with white. Head, mantle edge and branchial lamellte black. 

 Head very long, not large in proportion ; muzzle small. Ten- 

 tacles short, slender, pointed. Branchial lamellse not semicir- 

 cular, as in most Patellie, but produced, twisted, and elongated, 

 having, upon a superficial examination, an arborescent appear- 

 ance. They are very slightly smaller in front. Radula with a 

 well developed median tooth. Cusps of the teeth fawn color, 

 with chestnut brown bosses and an orange ring at the point of 

 insertion of the cusp. Formula, 1 



^ 3(i/^_-2-2-i4)3- 



Shell white, inside and out, sometimes with a rusty or green- 

 ish stain here and there, and furnished with obsolete radiating 

 ribs. Often attaining a length of from eight to fourteen inches. 



This magnificent limpet, the largest non-spiral gasteropod now 

 iving, proved, as might have been anticipated, to differ essen- 

 tially from its smaller cousins. It is found in Central America. 

 The radula figured was from an Acapulco specimen. It is some- 

 what singular that the animal of a nearly white shell should be 

 almost bhick, especially as the shell is an external one. I have 

 seen the latter frequently used as a wash-basin, in Central 

 America. 



Genus PATELLA, Liune. 



Patella, Auct. omn. binom. P. vulgata, type. 

 Patella, Lam., Prodr. 1799. P. granularls, type. Syst. 

 An. s. Vert. ed. 1801. P. testudinaria, type. 

 < Patella, Lin., Syst. Nat. 1758, ed. x. H. and A. Ad., Gen. 

 Rec. Moll, i, p. 464. Cpr., Lect. Moll. p. 71. Gray, 

 Guide, p. 174. P. Z. S. 1847, p. 168. Woodw., Man. 

 p. 154. Schum., Essai, 1817. 



* From AyKia-Tfov, a hook or claw, aud Mfcr»jif, middle. 



