Notes on the Classification of the Corbicidadce, etc. 421 



and the exotic species have none. The sinus of the Corbicula, 

 I will note, is usually shorter and less sinuous than that of 

 Cyrena. I refer to the annexed figures of Corbicula obsoleta, 

 from South America, and of Corbicula Largillierti, from 

 China. 



So far I have spoken only of the recent species of Cyrena 

 and Corbicula ; one fossil species of Corbicula from America, 

 the Corbicula densata 1 Conrad, I am informed by Mr. Conrad, 

 possesses no sinus ; I have not had an opportunity of examin- 

 ing the shell myself. In this connexion I will mention that 

 three fossil species of the genus Corbicula from the Basin of 

 Paris, which I have in my possession, the Corbicula antiqua, 

 cuneiformis and Forbesii, show certainly a very marked 

 indentation in the region where the palleal impression is 

 joined to the posterior adductor muscle. The figure of Corbi- 

 cula antiqua will exhibit what I refer to. 



With regard to Velorita, of the three species known, I have 

 examined two, the one represented below, and Velorita par- 

 vida, and they certainly exhibit indications of a sinus. 



Fig. 6. 



Fig. 5. 



Corbicula antiqua (fossil), from the 

 Basin of Paris. 



Velorita Cochinensts, 

 from Cochinchina. 



The presence or absence of a sinus has always been consi- 

 dered a generic distinction, and it may be necessary to subdi- 

 vide the Corbiculadge according to this test. It behoves us, 

 however, to be cautious, because it is possible that too much 

 importance has been attached to this feature. 



APRIL, 1S67. 31 Ann. Lto. Nat. Hist. Vol. VIII. 



