PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 337 



California as far south as the Santa Barbara Islands, from low-water 

 mark to eighty fathoms, Dall ! Seventy -four specimens examined. 



I showed in 1871 that this species has nothing in common with the 

 genus Scurrta, to which it has often been referred, except a very super- 

 ficial resemblance of form of the shell. It is not very abundant any- 

 where. The partially striated variety tenuiscutyta Opr. has not been 

 found in Alaska. A. mitra varies from white to pink or green, and is 

 frequently covered with regular nodules or papillae of nullipore, when 

 it is A. mammillata of Eschscholtz. It is the most unmistakable shell 

 of the genus, the members of the restricted subgenus Acmcca presenting 

 a singular contrast with one another in respect to their shelly covering. 



Acmsea insessa. 



Patella insessa Hinds, An. Nat. Hist, x, p. 82, pi. vi, f. 3. 

 Acmcca insessa Dall, 1. c. p. 244, pi. 14, f. 3. 



Hab. — Sitka Harbor (one specimen), southward to San Diego, Cali- 

 fornia, Dall! Thirty specimens, mostly from the beaches. It seems 

 very rare in Alaska. 



Acmeea instabilis. 



Patella instabilis Gould, Proc. Boston Soc. Nat. Hist, ii, p. 150, 1846. 

 Acmwa (?) instabilis Dall, 1. c. p. 245. 



Hab.— Sitka, Fort Wrangell, very rare; southward to Vancouver 

 (abundant), and Monterey, Cal. (rare) ; dead on beaches. 



This species, like the last, lives on the stems of the giant fuci com- 

 mon to this coast, and I have never seen a fresh specimen with the soft 

 parts. But a radula extracted from one by Mr. H. Hemphill, and kindly 

 sent to me, enables me to say with confidence that it is a typical Acmcecu. 



Extra-limital Species. 



Acmeea rubella. 



Patella rubella Fabr. Fauna Gronl. p. 386, 1780. 

 Pilidiumfuluum (pars) Dall, Am. J. Conch, v, part iii, 1869. 

 Tectum (Erginus) rubella Jeffreys, Ann. Mag. Nat. Hist. p. 231, Mar. 1877. 

 Tectura rubella G. O. Sara. 1. c. p. 121, pi. 8, f. 5 a-b, pi. ii, f. 11, 1878. 

 Bab.— Greenland, Fabr., Moller, Jeffreys; Norway, inFinmark, Sars^ 

 5 to 40 fathoms. 



The shell is generally of a much more brilliant orange color than the 

 Pilidium, with which it has been confounded. I am not sure that some 

 very young and minute specimens of Limpets found in the Aleutian 

 Islands may not belong to this species, but they are too small to deter- 

 mine their relations with any certainty. 



It is unfortunate that Prof. Sars, while recognizing in part the char- 

 acters which I used to separate this subgenus from Collisella in the 

 genus Acmcca in 1871, should have applied the name Tectura to the true 

 Acmoeas, and used Acmcca for Collisella, in his very valuable work on the 

 Arctic Mollusks of Norway ; thus exactly reversing the original arrange- 

 ment and inadvertently transgressing the laws of nomenclature. 

 Proc. Nat, Mus. 78 22 Feb. 14, 1 870. 



