CONCHIFERA. 



261 



dulations, is reflected at the margins. This reflected 

 extremity is left entire at certain periods of growth, and 

 the tube is recommenced according to the necessities of 

 the animal. Some specimens have been found with four 

 or five of these entire reflections."* They live buried in 

 the sand of the shore, and place themselves perpen- 

 dicularly. When they ascend, the narrow end appears 

 first; this contains the siphons by which the animal re- 

 ceives and rejects the water so necessary to its existence; 

 these are attached to the tube at the point where the 

 small valves are situated. 



Family 9. — CARD I A CEA. 



The animal has the mantle cloven more than half way, 

 the back part beset with cirri, and running out into two 

 short tubes ; the foot varies in the genera ; the shell is 

 equivalve, heart-shaped, with prominent bosses ; the liga- 

 ment is exterior, two muscular impressions, and the pallial 

 impression without a sinus. Living in the seas of all 

 zones. 



Cardium. Lin. — Shell more or 

 usually inflated in form, equivalve, 

 nearly equilateral, posterior side some- 

 times gaping ; the exterior is seldom 

 smooth, generally radiatedly ribbed, 

 and the borders of the valves toothed 

 and plaited, and locking into each 

 other; two cardinal and two lateral 

 teeth in each valve, ligament exterior, 

 bosses prominent. Animal, suborbi- 



less heart-shaped, 



Cardium edide. 



* Reeve's Con. Sys. 



s 3 



