PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 335 



(Fisher!) to Puget Sound, W. T. (Swan and Kennerly!). Abundant 

 fi'om 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 typical 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. cceca by authors. It has not yet been found north of the Aleutians. 



C. concentrica var. instabilis. 



f Cryptobrancliia instabilis Dall, I. c. p. 145, pi. 15, f. 6. 



I am now convinced 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, from living on the stalk of Nereocystis, has become 

 peculiarly arcuated and greatly thickened, much like Acmcea instabilis, 

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

 numbers, dead, in 10-15 fathoms. 



Cryptobranchia alba. * 



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



Sab. — Plover Bay, E. Sib., Dall! Seniavine Straits, Stimpson! 

 Akutan Pass, Aleutian Islands, Dall ! 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. 

 cceca and C. 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 -Jim ita I Spec ies. 

 Subgenus Pilidiu3I Forbes. 



Pilidium Forbes, Athenajum, Oct, 6, 1849, p. 1018.— Forbes & Hanley, Brit. Moll, ii, 

 p. 440, 1849; not of Middendorf, Sib. Reise, p. 214, 1851.— Dall, L 0. 1889 

 (synonymy, etc., in full). 



Iothia Gray, not Forbes, ia54 (cf. Dall, L c. 1869). 



Teciura Jeffreys, 1865, not of Gray (1847), nor of authors. 



Sett tell ina Chenu (pars), Sars, not of Gray, 1847. 



Pilidium fulvum. 



Patella fulra O. F. Miiller, Prodr. Zool. Dan. p. 227, 1776. 

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

 Pilidium rubellum Stm. Checklist Sh. N. Am. E. Coast, No. 312, I860. 

 Tecturafulva Jeffreys, Br. Conch, iii, p. 250, 1865. 

 * Patella forbesii J. Smith, Wern. Soc. Mem. viii, p. 107, pi. ii, f. 3. 

 Scutellina fulva G. O. Sars, Moll. Reg. Arct. Norv. p. 122, 1878. 



Eab.—^oTthern and Arctic seas of Eastern America and Europe; 

 doubtfully reported from the Adriatic, where, if it be correctly identified, 



