PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 339 



proven. Other varieties, almost without number, might be selected from 

 the series before me, which taken singly seem quite as distinct, and it. 

 seems preferable to err, if at all, in the matter of Darning mere varia- 

 tions, on the side of conservatism. 



Acmaea (Collisella) persona. 



Aem(Pa persona Eschsclioltz, Rathke, 1. c. p. 20, pL xxiv, f. 1-2, 1833. — Dall, 



L c. p. 250, pi. 14, £ a 

 Tectum digitalis von Martens. 1. c. p. 93, t. 3, f. 3-4. 

 Tectum persona lb. L c. p. 95, f. 5, 6. 



Hah. — Adakh Id., Aleutians (one specimen), Shumagins. Cook's Inlet 

 (Martens), Port Etches, and southward to California as far as the Santa 

 Barbara Islands, between and sometimes above tide-marks. One hun- 

 dred and twenty-eight specimens collected. 



The varieties of this shell are often very beautiful, and, taken by them- 

 selves, apparently well marked ; but in a large series these differenced 

 disappear in the general interchange of characters in a way which is 

 impossible to fully realize without a very large series. The synonymy 

 will be found in my paper above cited, and contains several variations 

 much more striking than those separated by von Martens. 



Acmaea (Collisella) testudinalis. 



Patella testudinalis Miffl. Prodr. Zool. Dan. p. 237, 17G6. 

 Collisella t. Dall, 1. c p. 249, pi. 14, t 13, 1871. 



This well-known form was supposed by me to be pretty easily sepa- 

 rable from C. patina Esch. in 1871, but the result of several years' addi- 

 tional study of the region about the Aleutian Islands has rudely shaken 

 that cherished belief. There is a pretty constant difference in the rela- 

 tive size and proportion of the teeth on the radula of large and fully 

 grown specimens; but of other characters (with seven hundred and thirty 

 specimens before me of all sizes, ages, and localities) I find it impossible 

 to formulate any. Dr. Carpenter at one tune thought them distinct, but 

 a re-examination by him resulted in his confessing his inability to dis- 

 tinguish one species from the other by the shells, and I can confidently 

 assert that the exterior of the animals affords no characters whatever. 

 Indeed, some of the varieties of what we have called typical patina are 

 more different from the type than test nd in alia can possibly claim to be. 

 Specimens of adult patina from Sitka and the Aleutian Islands are 

 indistinguishable from specimens of testudinalis of the same size from 

 Eastport, Maine. It has been found impossible to rightly assort a mixed 

 lot by every one who has tried it. I am therefore forced to divide the 

 species as follows : 



Collisella testudinalis var. testudinalis. 



Hah. — In Alaska from the Arctic Ocean southward (on both sides of 

 Bering Sea) to Sitka. On the eastern coast of America from Long 

 Island Sound to the Arctic Ocean, Cumberland Gulf (Kumlein), and 

 South Greenland. In Europe, it extends from the English Channel 



