PANAMIC-PACIFIC PELECYPODA 169 



The hinge line of this species is very much like that of P. (Pseuda- 

 musium) thalassimus Dall described in the "Blake" report. (Dall, 1908). 



This species will be recognized by its small size, nearly circular form, 

 except along the dorsal side which has a small triangular beak and large, 

 subequal ears. Inner surface of valve plain, no lirae showing. The ears have 

 a large, impressed, flattened inner surface which is finely vertically grooved 

 or striated along the hinge, these groovings often interlock so well that the 

 valves do not separate easily without breaking the shell. 



Range — Cedros Island, Lower California to Panama. For numerous 

 records along the coast of Mexico and Costa Rica, see Hertlein and Strong. 

 Panama. Panama Bay (Dall). Drift shells on beach, Playa Marinero just 

 west of Guanico. 



Superfamily LIMACEA 

 Family LIMIDAE 



Shell monomyarian or with a single adductor scar, obliquely sub- 

 pectiniform with small, narrow ears and median beaks, equivalved, inequi- 

 lateral, the shorter side being posterior, usually white, externall}'^ sculptured 

 with fine or coarse, generally scabrous radial riblets. Lateral margins gen- 

 erally thickened, the anterior one with an open gap. Hinge line straight, 

 edentulous, or with obscure denticulations on the side, the cardinal area 

 high, subtriangular with a central resilial pit under the beak in each valve. 

 A thin brown deciduous periostracum is often present. 



But three shallow-water species of Lima appear to be regional in the 

 southern part of the Panama-Pacific faunal province. Two deep-water 

 species have been described: L. agassizi Dall from the Gulf of Panama and 

 L. diomedae Dall from off the Galapagos. These belong to the subgenus 

 Acesta, species of which may reach a large size. 



Key to the species of Lima in the southern portion of the Panama- 

 Pacific faunal province. 



A. Valves rather thick and heavy, the anterior side straight and strongly 

 flattened. Ribs strong, straight, coarsely scaly. 



Lima (Li/ma) tetrica 



B. Valves thin, the anterior side not flattened, Ribs fine. 



1. Valves convex, inflated, the margins closed, the lateral gap if any 

 very small. 



Lima (SuhmanteUum) orbignyi 



2. Valves flexed, widely gaping on both sides, in contact only at the hinge 

 and along the ventral margin. 



LimM' (Promantellum) pacifica 



Genus LIMA Bruguiere, 1797 



Type species by monotypy, Ostrea lim^ Linne. 



Valves compressed to slightly convex, thick-shelled. Anterior side 

 straight, strongly impressed or flattened, the anterior ear small. Ribs 

 relatively few, large, straight and coarsely scaly. 



Lima (Lima) tetrica Gould Plate 17, figure 4 



Lima tetrica Gould, 1851, Proc. Boston Soc. Nat. Hist, vol. 4, p. 93.— Gould, 1857, 

 Jour. Boston Soc. Nat. Hist., vol. 6, p. 405, pi. 16, fig. 6.— Durhann, 1950, Mem. 

 Geol. Soc. America, No. 43, pt. 2, pp. 67, 68, pi. 11, figs. 2, 3. 



Lima (Lima) tetrica Gould, Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 65. 



