PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 339 



proveu. 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 naming mere varia- 

 tions, on the side of conservatism. 



Acmaea (Collisella) persona. 



Acmwa persona Eschsclioltz, Ratlike, 1. c. p. 20, pi. xxiv, f. 1-2, 1833. — Dall, 



1. c. p. 250, pi. 14, f. 8. 

 Tectiira digitalis vou Martens, 1. c. p. 93, t. 3, f. 3-4. 

 Tectura peisoiia lb. 1. o. 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 beautifid, and, taken by them- 

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

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

 impossible to full^' 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. 



Fah'lla testudinalis Miill. Prodr. Zool. Dan. p. 237, 1766. 

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



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

 rable from C. imtma 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 aU sizes, ages, and localities) I find it impossible 

 to formidate any. Dr. Carjienter at one time thought them distinct, but 

 a re-examination hy 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 testudinalis 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. 



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

 Bermg 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 



