340 AMERICAN JOURNAL 



ture. The young is- extremely inequilateral, and rapidly de- 

 velopes the characteristic ribs. Inside, the shell has a white 

 callus, through which the dark irregular blotch appears. 

 This occasionally takes the form, so common in Valparaiso 

 limpets, of irregular ghostly bars, which gave the name to 

 the species. Many of the Valparaiso shells of the United 

 States Exploring Expedition were named Oregona (=persona) 

 by Mr. Cuming, having exactly the same shape, and, with 

 that species, often presenting the spectral appearance. It ap- 

 pears, therefore, that neither shape, nor color, nor sculpture 

 alone suffice in all cases to separate the limpets of North and 

 South America, nor the North American species from each 

 other. I generally find the best guide to be a certain habit of 

 growth, which presents a balance among the individual char- 

 acters. I confess that I could not always separate Northern 

 and Southern individuals, either of the scutum or the Oregona 

 types, in a mixed collection, unless they were in very good 

 condition. Even Mr. Cuming had the same difficulty. The 

 general run of specimens, however, can generally be distin- 

 guished, without much risk of error. 



Acmjea scabra, (Nutt.,) Reeve, (non Gld.) 



This species is also so well marked, that it has not been re- 

 described.. It is rare, and confined to the Southern fauna, 

 ranging (like spectrum) from Lower California to Monterey. 

 With the shape and size of A. patina, it is easily distinguished 

 by the crowded, imbricated riblets, which may almost always 

 be traced near the margin, even when the surface is decortica- 

 ted. The shell is thin, and normally of an orange-tinted 

 white, generally faintly spotted outside and dotted near the 

 margin with rufous. The margin is sharp and spreading ; 

 the interior china-white, or with rufous spots, and sometimes 

 a bluish tinge anteriorly. The nuclear shell is of a reddish 

 horn-color, extremely thin; when a little older, the apex is, as 

 usual, very anterior, the rasp-like surface most delicately 

 sculptured, and the color finely gauzed with rufous. 



A well-marked variety seems to have an admixture of black 

 blood, probably from intermarriage with the negro race of A. 

 patina. With the same sculpture externally, the interior has 

 the broad black margin of A. patina, (var. scutum,) and a dark 

 spot in the centre. One specimen is dark all over. Another 

 stout dwarfed shell has a prettily tesselat 3d boorder, and would 

 (in a mixed collection) be taken for A.cymhiola, Gld.,=P. para- 

 sitica, D'Orb. — As I have seen no intermediate specimens be- 

 tween the two forms, this may be described as var. limatula, 

 4 A. scabra, Nutt.," extus sculpturu normali ; seu intensiore, 



