Mytilidae and Periplomatidae 55 



pronounced posteriorly; interior white. 



This is a boring species. Sometimes found in lumps of coral on 

 the beach, dredged in living coral and in rock from reefs. 



Lithophag^ bisuloata^e (d'Orbigny) PI. 8, fig. 43 



Alt., 11; length, 38 mm. Shell with polished brown epidermis, 

 usually covered with a rough, brownish-colored calcareous coating; 

 shell date-shaped; posterior margin smoothly rounded, but epidermis 

 and its calcareous coating prolonged beyond the rounded shell mar- 

 gin to a blunt point. Umbos small, pointed, at anterior end of hinge 

 margin. Each valve has two oblique sulcations directed posteriorly 

 from dorsal margm. Interior brown. 



Burrows in coral, rock, other shells, cement. Found in both 

 shallow and deep water. 



Lithophaga aristata" (Dillwyn) PI. S, fig. 44 



Alt., 14; length, 30 mm. Shell cylindrical, dull white, brittle, 

 similar to L. bisulcata in shape and general character; no sulca- 

 tion of valves; the posterior prolongations of the valves cross in 

 a scissorlike manner. The mollusk burrows m coral. 



Genus 3I0I)I0LARIA Beck, 1938 

 Modiolaria^s lateralis (Say) PI. 8, fig. 45 



Alt., 5.5; length, 12 mm. Thin, fragile, pale brown, with thin, 

 shining epidermis; shell inflated, slightly carinate posteriorly. Umbos 

 small, rounded, recurved; valves finely ribbed at each end with a 

 smooth central area; margins serrate at ends of ribs, smooth with 

 byssal notch between groups of serrations; pearly lining. 



Usually attached to ascidians, in the crevices of zooid colonies, 

 on shells such as Atrina. 



Order AN0MAL0DES3IACEA =^9 

 Family PERIPLOMATIDAE 



The east American genera of the Periplomatidae are distributed 

 along the coast from Labrador to Florida and the West Indies. The 



^^ Lat., bis, twice; sulcare, to furrow. 



^' Lat., arista, arm. 



^8 Lat., modiolus, with suffix arius to form generic name. 



^9 Gr., anomalos, uneven; desmos, band or ligament. 



