^"l89o!"'J PROCEEDINGS OF THE l^ATIONAL MUSEUM. 223 



Two specimens are contained in the National collection (Museum No. 

 105391), the largest of which measures from the beaks to the ventral 

 margin or edge 36""", from the anterior to the posterior edges in the 

 broadest place il"""", and the thickness or diameter is 14.50"'"\ 



Habitat. — San Pedro, Long Beach, etc., Los Angeles County, Cali- 

 fornia ; Mrs. M. Burton Williamson and others. 



This is an unusual form for a member of the Anatina group, and quite 

 distinct from any of the West coast representatives of the family hereto- 

 fore described. 



The Anatina (Periploma) alta C. B. Ad. (Panama shells, p. 294:), de- 

 cribed from a single valve, is a transverse form, the measurements as 

 given by the author being as follows: " Length, 1.98 ; beight, 1.35; 

 breadth 0.7 inch.," or nearly seven-tenths (0.G7) of an inch more from 

 the anterior to the posterior margin than from the beaks to the ventral 

 or opposite edge of the shell. 



This should not be confounded with P. alta Conrad (Proc. Acad. Nat. 

 Sci. Phila., p. 585, 1862, Am. Journ. Conch. II, p. 70, pi. 4, fig. 10,= P. 

 peralta Conr., Am. Journ., Conch, iii, p. 188, Sept., 1867), from the Mio- 

 cene of New Jersey, which is a rounded form not unlike P. discus in 

 general appearance. 



Pervploma excurva Cpr. is also a transversely elongated form, though 

 less inequilateral than the foregoing, and measures, as quoted, " long. 

 2.06; lat. 2.46; alt. 1.05 poll." 



Periploma paijyracea Cpr,, described by the author from one " perfect 

 valve and a broken pair displaying the hinge in situ are all that is known 

 of this beautiful species. It differs from the others in its outline, the 

 greater part of which is suborbicular, with a short broad beak." 



The dimensions are given as "long. 0.78; lat. 1.06, alt. 0.42 poll." 



P. excurva and P. papyracea are both described on page 229 of the 

 Proceedings Zoological Society of London, with many other forms 

 " principally in the collection of Hugh Cuming." P. papyracea is, it will 

 be seen, somewhat more equilateral than P. excurva, yet much less so 

 than P. discus. 



In Carpenter's British Association Report (1856), on page 287, he 

 erroneously refers to P. excurva as "P. excurvata." Periploma argentaria 

 Conrad is the name usually given to the commonest of the west Ameri- 

 can species ; it was described by the author in 1837.* Dr. Gould re- 

 garded the shell described by Conrad as the same to which Sowerby had 

 given the name of planiuscula in 1834.t In the same place Sowerby has 

 described still another species, P. lenticularis, from the island of Mu- 

 erte, which is in the Bay of Guayaquil, about 3 degrees south latitude. 

 The examples of P. 2)1 aniuscul a described by Sowerby were collected at 

 St. Elena, a point on the northerly boundary of the same gulf, and both 

 of these species by Cuming. Carpenter makes no allusion to lenticularis 



* Jour. Phila. Acad. Nat. Sciences, Vol. vii. Part ii, 1837, p. 238., PI. 18, Fig. 8. 

 tProc. Zool. Society London, 1834, p. 87. 



