PANAMIC-PACIFIC PELECYPODA 229 



and degeneracy. The genera are classed together here largely for convenience 

 of treatment rather than on a basis of common affinities with each other. 



Some species of Panamic leptons are locally common and can be ob- 

 tained in good series, such as Aligena cokeri and Bornia zorritensis, others 

 are rare and known only from a few specimens, hence, this treatment of 

 the group is admittedly incomplete and major additions can be expected 

 in the future. Although work on the Erycinacea is specialized and difficult, 

 they are nevertheless of great interest and well worth the attention of the 

 qualified naturalist. 



Family ERTCINTDAE 

 Genus ERTCDfA Lamarck, 1805 



Type species by subsequent designation, Stoliczka, 1871, E. pellucida 

 Lamarck. 



Shell small, white, ovate, oblong or subelliptical, subequivalve, thin, 

 depressed or slightly convex. Ligament internal, lodged in a small, elongate 

 resilifer behind the beak and under the shell margin. In front of the resilifer, 

 there is a small, inclined tooth which in some instances may be obsolete; 

 lateral teeth are variable in size and strength; in the right valve, the 

 laterals are represented by sockets with elevated basal rims, placed equi- 

 distant from the beak; pallial line simple. Surface smooth or marked with 

 fine, concentric growth lines and sometimes with fine radial striations. 



Erycina eolpolea Dall Plate 36, figures 5, 5a 



Erycina eolpolea Dall, 1913, Proc. U. S. Nat. Museum, vol. 45, No. 2002, p. 596. Beach 

 at the head of the Gulf of California. — Dall, 1925, Proc. U. S. Nat. Museum, 

 vol. 66, art. 17, p. 16, pi. 27, fig. 2. — Hertlein and Strong, 1947, Zoologica, vol. 

 31, pt. 4, pp. 132, 133. 



Shell small, white, equivalve, very inequilateral, the anterior end much 

 the longer and somewhat expanded, posterior shorter and smaller, both 

 rounded; dorsal and basal margins slightly arcuate, subparallel; surface 

 sculptured only with concentric incremental lines, covered with a thin, pale, 

 yellowish periostracum; beaks low, inconspicuous, valves rather compressed; 

 interior polished, hinge formula lo.Ol.olo; chondrophore very narrow, ob- 



"^l.lO.lol 

 lique, and posteriorly directed. Length of shell, 10, of anterior part, 8, height 

 6, diameter, 3.5 mm. (Dall, 1913.) 



Range — Gulf of California to Panama. Mexico: Gulf of California 

 (Dall); Port Guatulco (Hertlein and Strong). Nicaragua: Corinto (in beach 

 drift and at a depth of 12-13 fms.) abundant (Hertlein and Strong). 

 Panama: off Taboga Island (dredgings) Mr. Lee Beil. 



Family LEPTOXLDAE 



Tlie shell is small, free, with equal valves, their margins smooth, closed 

 tightly or with a small gap, the surface smooth or with radial sculpture. The 

 ligament is mostly internal. Hinge variable, normally with one or two 

 cardinal teeth and a pair of lateral teeth in each valve; the anterior lateral 

 tooth is sometimes lacking, while the posterior lateral tooth is often so 

 closely adjacent to the resilifer as to resemble a cardinal. The species are 

 generally ovoviviparous. 



