Notes on the Classification of the Corhiculadce, etc. 419 



It is not my object at present to propose any modification in 

 the classification now used ; in fact, I think that in the actual 

 state of our knowledge of the soft parts of Corbiculadae, any 

 change introduced would be inopportune at this moment, and 

 only lead to future confusion, without producing any perma- 

 nent benefit. What I have in view is to call attention to cer- 

 tain characters derived from the soft parts, indicated, however, 

 by an examination of the shell, and the existence of which 

 has, as yet, not been sufficiently noted. 



Formerly all the species of Corbiculadas were looked upon 

 as having a continuous palleal impression, and the family was 

 always described as such ; it was only when attention was 

 turned to American Corbiculadae, that it was noticed that cer- 

 tain species of Cyrena and Corbicula showed a palleal impres- 

 sion with a sinus. 



I am speaking now more particularly of the genera Cyrena 

 and Corbicula, as all the species of Batissa, Sphserinm, and 

 Pisidium, show an unbroken palleal impression. As regards 

 Yelorita, I will say a few words later. 



All the American species of Cyrena that have passed through 

 my hands, exhibit a sinus, commonly long and sinuous ; 

 in all the exotic species I have seen the sinus is absent. 



Fio. 1. 



Cyrena fortis, from Ecuador. 



