OSTREIDAE 43 



lateral transverse folds in a pectinate arrangement from midrib to 

 margins. The attached valve bears several curved processes which 

 embrace the stem of a gorgonian or some other twiglike support, 

 and attach the shell securely in its long axis. Shell margins deeply 

 serrate, points interlocking; interior white, polished; hinge, muscu- 

 lar impression and pallial Ime typical. 



Dredged in four to six fathoms — usually about reefs. 



Ostrea crislata-^ Born (O. spreta d'Orbigny) PI- 4, fig. 21 



Alt., 40; length, 40 mm. Irregular, often rounded, attached 

 valve deep, free valve rather flattened; surface of both valves folded 

 into deep, radiate plications which extend to margin of shell and 

 there form acute, interlocking serrations. Umbo of attached valve 

 definitely longer than its fellow. Interior white, polished; often a 

 callus deposit at site of the single muscle scar. Clasping processes 

 similar to those of 0. frons are developed in the lower valve, but are 

 frequently expanded into pillarlike attachments when the shell rests 

 upon a flat surface — often valves of Atrina and Pteria. 



Dredged with 0. frons. 

 Ostrea perniollis^o Sowerby PI. 4, fig. 22 



Alt., 30; length, 20-26 mm. Shell flattened, variable in shape 

 and outline, usually rounded but sometimes almost quadrangular. 

 Moderately thin, translucent, golden color with delicate epidermis; 

 parts of the shell which are exposed lack the golden hue. Almost 

 equivalve, umbos flattened to plane of valves and abruptly recurved 

 to right and left on respective valves. Distinct growth lines; interior 

 white. This oyster lives embedded in the substance of the "bread 

 sponge". 



Genus CRASSOSTREA Sacco, 1897 

 Crassostrea yirginica (Gmelin) {Ostrea virginica Gmelin) PI. 4, fig. 19 



Size variable according to locality and food supply; shape ir- 

 regular-elongate, sometimes nearly circular. The shell is fixed at the 

 umbonal region of the left valve which is larger and deeper, but 



-^ Lat., cristatus, crested. 



3*' Lat., per, very; mollis, soft. 



