PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 335 



(Fisher!) to Piiget Somid, W. T. (Swau and Kennerly!). Abundant 

 from low water to eighty fathoms on stones and shells, sometimes attain- 

 ing the length of an inch, but usually about four-tenths of an inch long. 

 Five hundred and twenty-seven specimens examined. 



This is the largest and most abundant species of the family. In it, 

 beside differences in dentition, the apex is simply pointed or blunt, not 

 deciduous, as in the tyi)ical Lepeta. The sculpture is usually faint, but 

 sometimes raised in beautiful concentric frills, from which the name was 

 derived. Small specimens from slight examination have been quoted as 

 L. ccvca by authors. It has not yet been found north of the Aleutians. 



C. concentrica var. instabilis. 



f CryptohrancMa instalilis Dall, 1. c. p. 14r), pL 15, f. 6, 

 I am now con\inced that the provisional name which I applied to this 

 singular form is only of varietal value. It seems, from later specimens, 

 to be a form which, fiom living on the stalk of Nereocystis, has become 

 peculiarly arcuated and greatly thickened, much like Acmari insfahiUs, 

 which has the same habit. It has only been foimd at Sitka in small 

 numbers, dead, in 10-15 fathoms. 



Cryptobranchia alba. 



C. alba Dall, 1. c. p. 145, pi. 15, f. 3 a-d, 1869. 



I];ah. — Plover Bay, E. Sib., DaU! Seniavine Straits, Stimpson! 

 Akutan Pass, Aleutian Islands, DaU ! Dead on beach. Alive at six- 

 teen fathoms, gravel. Twenty-four specimens examined. 



This species appears to fill the gap between the distribution of L. 

 cccca and G. concentrica. It is easily distinguished from the latter by its 

 smooth surface and rounded apex and back, beside anatomical charac- 

 ters. It rarely reaches nearly an inch in length, and is of the purest 



whiteness. 



Extra-limital Species. 



Subgenus Pilidium Forbes. 



Pilidium Forbes, Athenaum, Oct. G, 1849, p. 1018.— Forbes & Hanley, Brit. Moll, ii, 

 p. 440, 1849 ; not of Middeudorf, Sib. Eeise, p. 214, 1851.— Dall, 1. c. 1869 

 (synonymy, etc., in full). 



lothia Gray, not Forbes, 1854 (cf. Dall, 1. c. 1869). 



Teciura Jeffi-cys, 1865, not of Gray (1847), nor of authors. 



SaitcUina Chenu (pars), Sars, not of Gray, 1847. 



Pilidium fulvum. 



Patella fitha 0. F. Miiller, Prodr. Zool. Dan. p. 227, 1776. 



Pilidium fulvum Forbes, Athenreum, 1, c. Oct. 6, 1849.— Dall, 1. c. 1869. 



Pilidium ruhellum Stm. Checklist Sh. N. Am. E. Coast, No. 312, 1865. 



lecturafulva Jeffreys, Br. Couch, iii, p. 250, 1865. 



Patella farhesii J. Smith, Worn. Soe. Mem. viii, p. 107, pi. ii, f. 3. 



Scutcllinafulva G. 0. Sars, Moll. Reg. Arct. Norv. p. 122, 1878. 



Sab. — Xorthern and Arctic seas of Eastern America and Europe; 

 doubtfully re]3orted from the Adriatic, where, if it be correctly identified, 



