CONCHOLOGY. 39 



A. lucinalis. A. purpurascens. 



A. Boysii. A. nucleola. 



A. tenuis. A. physioides. 



A. glahrella. The smooth Amphidesma. PI. 6, fig. 9. 

 Species lenticular or oval, with or without a lunated de- 

 pression. 



A. lactea. The milky Amphidesma. 

 Sub-orbicular, sub-pellucid, compressed, reticulated ; yel- 

 lowish white. 



FAMILY VI. 



CoRBULACEA. Two genera. 



I. Corbula. Nine species. 

 This genus approximates the Crassatella and Ungulina, 

 but is distinguished from them by the inequality of the valves 

 and the strong primary tooth. 



Shell rather solid, a little irregular and triangular, ine- 

 quivalve, more or less inequilateral, rounded and enlarged 

 before, attenuated and prolonged behind ; summits well 

 marked, one projecting behind the other ; hinge anomalous, 

 formed by a large, conical, recurved cardinal tooth, with a 

 cavity at its base for the reception of the tooth of the other 

 valve ; ligament very small ; two muscular impressions Kttle 

 distant. 



Corbula Australis. Corbula Taitensis. 



C. sulcata. C. nucleus. 



C. erythrodon. C. impressa. 



C. ovalina. C. porcina. 



C. semen. 



C. nucleus. The kernel Corbula. 



Strong, sub-triangular, under valve larger than the upper 

 one ; transversely striated ; covered with a thick brownish 

 epidermis. 



C. ovalina. The ovate Corbula. PI. 6, fig. 6. 

 Regular species. 



