PANAMIC-PACIFIC PELECYPODA 419 



them produced to a narrowly truncate end. Surface sculpture consists of 

 12 or more, deep, parallel undulations which terminate sharply at the 

 anterior and anterior-ventral margins as if cut off, the undulations because of 

 the thinness of the valves show clearly in the interior and generally undulate 

 the anterior margins. 



A rare species, easily recognized by its sculpture. Usually less than 

 16 mm. in length. Fossil in the Pliocene of Ecuador. 



Range — Gulf of California to Ecuador. Panama: Lagartillo, near Las 

 Tablas; South Passage, Pearl Islands (Hertlein and Strong). Ecuador: 

 Esmeraldas; Manta; Santa Elena. 



Genus AUSTKOMACOMA, new genus 

 Type species, Macoma constrict a (Bruguiere). Caribbean and south 

 Florida. 



Shell subovate, fairly convex, generally thin, the posterior side weakly 

 or strongly flexed towards the right, the left valve as a result somewhat 

 larger and more inflated than the right. Two cardinal teeth in each valve, 

 the posterior right and the anterior left teeth bifid; lateral teeth absent. 

 Ligament entirely external, attached to a long, slender scar behind the 

 cardinal teeth; no nymphal ridge. The anterior adductor scar is long and 

 narrow, lucinoid, with the pallial line attached to its lower end and follows 

 close to the ventral margin. Pallial sinus large, somewhat discrepant in 

 the two valves, widely coalescent with the pallial line below. Surface white, 

 marked with fine, hairlike concentric threads and covered with a thin 

 hght-colored periostracum. 



Typical Austromacoma has a large pallial sinus, high and pointed 

 under the beak, and connected with the anterior adductor scar at its lower 

 end. The genus appears to be restricted to the Caribbean. 

 Order ADAFEDONTIDA 

 Superfamily SOLEIfACEA 

 Family SOLENIDAE 



Shells usually elongate, sword or razor-shaped, equivalve, usually 

 open and truncated at both ends. Beaks low, terminal or somewhat distant 

 from the anterior end, the posterior side always longer. Pallial sinus small 

 in species with anterior umbones, larger in those species having the um- 

 bones more distant from the end, the adductor scars large and well marked. 

 (Hinge relatively weak with one or two small cardinal teeth, more or less 

 projecting, the ligament external and attached to a short nymph. Surface 

 smooth or sculptured with concentric lines of growth, sometimes with 

 oblique striae or groovings, covered by a coarse brown or straw-colored 

 periostracum. Hinge plate often strengthened or buttressed by a thickened 

 ray. Burrowers in sand. 



Key to genera of the Solenidae 



L Shell straight or almost so. A single cardinal tooth in each valve. 



1. Beaks terminal, placed at the extreme anterior end. 



Genus Solen 



2. Beaks not fully terminal. 



Subgenus Solena 

 IL Shell with a decided curve. Hinge provided with two cardinal teeth 

 in the left valve. 



Genus Ensis 



