126 HELCIONISCUS. 



Patella nigrisquamata Reeve, Concii. Icon., f. 3, (1854). — 

 Patella mazatlandica Sowb., Zool. Beechey's Voy. Moll., p. 148, t. 

 39, f. 12, 1831. 



This species may be known by its erectly conical form, narrow 

 ribs, having close, high solid scales or nodules, of which some are 

 black, especially upon the upper part. The central area is small, 

 brown. The young (pi. 54, fig. 13) are spotted inside. 



The P. nigrisquamata of Reeve, is a shell exhibiting but little 

 variation. Reeve gives the locality " Australia," but this has not 

 been confirmed. One tray of the specimens before me are from 

 Concepcion, Chili, collected by Dr. W. S. W. Ruschenberger. The 

 others lack record of locality. 



The P. mazatlandica of Beechey's Voyage, was said to come from 

 Mazatlan, but this is of course a mistake. Carpenter at one time 

 referred it to one of the Californian Acmoeas as a synonym, but later 

 concurred in Hanley's opinion that it Avas the same as P. exarata 

 Nutt. This opinion I am not prepared to endorse, for the internal 

 central callus of P. exarata is white, or sometimes partly black or 

 violet-purple, but it is never, I believe, chestnut brown, as in the 

 figures and description of Mazatlandica, which correspond exactly 

 with young specimens oi nigrisqxiamata, now before me. 



The name mazatlandica has priority, but in view of the doubt 

 attaching to its use, and the fact that it is a misnomer, I have deemed 

 it wisest to retain Reeve's designation. 



Compare also Patella boninensis Pilsbry. 



The scattered black spots found on the upper part of the cone are 

 also seen in some specimens of P. exarata, and some other allied 

 species. 



(2). East Indian and Polynesian species. 



This region possesses species of two groups : strong, conical, rib- 

 bed species, such as exarata, argentata; and lower, more dehcately 

 sculptured forms, sagittata, tahitensis, testudinaria. The Chilian 

 forms are evidently derived from this fauna, and the Japanese 

 species are very closely allied, belonging to the same two groups. 



H. exaratus Nuttall. PI. 47, figs. 1, 2, 3, 6, 7, 8, 9, 10, 11, 12. 



Shell oval, conical, the apex slightly in front of the center ; slopes 

 nearly straight. Surface sculptured with many very strong black 

 ribs on a slightly lighter ground, the ribs subequal, about 38-48 in 



