212 



CASPIAN SEA. 



The remaining Mollusks are all forms of Cardium. 

 1. C. {Didacna) trigonoides. 2. C. (Didacna) Eich- 

 waldi. 3. C. (Monodacna) Caspicum. 4. C. {Mono- 

 dacna) pseudocardium. 5. C edide. 6. C. rusticum. 

 7. C. (Adacna)lceviusculum. 8. C. (A dacna) vitreum. 

 9. C. (A dacna) plicatum. 10. C. (A dacna) coloratura. 



1 and 2 are hardly distinct, and are most common 

 throughout the whole of the Caspian. Nos. 3 and 

 4 are considered by Middendorf to be nearly allied, 

 and Deshayes notices the resemblance of C. pseudo- 

 cardium to the common Cockle (C. edide). 

 Eichwald described the C. Caspicum from dead 

 shells, and doubts whether this species is now 

 living. The Caspian form of 0. edule is small, 

 but distinct. Dead shells of the variety C. rusticum 

 occur in abundance, but it is supposed that this 

 form may also have recently died out there. 



The following are rather south Caspian shells : 

 C. vitreum and G. Iceviuscidum, which latter is thrown 

 up after storms near Baku, in such quantities as to 

 serve as food for pigs, cormorants, and other water 

 birds. C. edentulum is found in the north Caspian, 

 but never living. C. plicatum occurs also in the 

 Black Sea, at the mouth of the Dnjestr, but is 

 there smaller than in the Caspian. C. coloratum 

 is common to the Black and Azof Seas, and to the 

 north Caspian. 



The shells of the genus Cardium (Cockles), so 

 numerous in all seas, as also at all past periods, 

 are throughout remarkable for the constancy of 



