336 AMERICAN JOURNAL 



Occasionally, almost the whole color of A, patina fades 

 away, and the shell developes the pinkish tinge of A. rosacea; 

 of this variety, a strangely distorted specimen is in the Mus. 

 Smithsonian. Sometimes the animal appears to perish from 

 atrophy, margin within margin appearing at the edge. 



The young shell is much flatter than that of A. pelta ; nor- 

 mally it has the apex very anterior, and the striae appearing 

 at an early age. 



ACMMA PELTA, Bsch. 



Zool. Atl., PL 5, p. 19.= P. fimbriata, Gld.= P. leucophsea, 

 (Nutt.) Rve. 



Junior=P. monticola, Nutt., pars-|- P. strigillata, Nutt., pars. 

 Yar. ?=A. cassis, Esch. loc. cit. p. 19. "Sitcha." 



This species, when in good condition, is easily recognized 

 by its regular conical form, narrow margin, and faint, irregu- 

 lar, bulging ribs ; but it is generally decorticated, and often 

 subject to remarkable variations of growth. Normally it is 

 painted with brown-olive, passing into black, in radiating 

 streaks (more or less broken-up into patches), which are deep- 

 est, tesselating the inner margin, between the ribs. Some- 

 times the ribs are strong and crowded from the commence- 

 ment; (in which state it may be the A. cassis, Eschscholtz, if 

 from Sitcha, as stated;) the shell then appearing, externally, 

 exactly like Patella deaurata, from Cape Horn. One of the 

 specimens sent to the Smithsonian Institution from the Cali- 

 fornia Academy actually belongs to that species, as do also 

 specimens brought to the British Museum, as from Vancouver 

 Island, by the British North Pacific Boundary Survey. No 

 doubt they really came from South America, and are easily 

 distinguished from all varieties of Northern limpets by the 

 rich metallic lustre of the inner surface. But sometimes the 

 ribs are nearly obsolete in the adolescent shell, only faintly 

 developing near the adult margin. Sometimes they fade 

 away, leaving nothing but blunt striae. The shell is then 

 known from the conical variety of A. patina by the narrow 

 internal margin, and (if perfect) by the non-striated upper 

 portion. Very rarely the shell loses its color, as well as its 

 ribs, when it closely resembles Scurria mitra; it can be distin- 

 guished, however, by its thin texture, and by some indication 

 of color or of striae in at least some portion of the surface. 

 The smoothness of the adolescent shell, as well as the dull 

 color, in which stripes prevail, is usually a good discrimi- 

 nating guide. In its first stage, like the other species, the 

 shell resembles a minute horny Ancylus, with the apex near 

 the margin. As the shell grows, the apex gradually ap. 



