CLASS OF THE CEPHAL.E. 



477 



developed vascular network ; but in general there exists a 

 very well developed branchial apparatus, composed of two 

 pairs of large membranous plates, finely striated, and floating 

 between the foot and the mantle (Fig. 458). The mouth is 

 also concealed between the folds of the mantle, and is found at 

 one of the extremities at the base of the abdomen ; it has 

 never any teeth, but is furnished laterally with two pairs of 

 labial prolongations, constituting laminated tentacles. The 



Fig. 461. Buccarde. 



Fig. 402.-Shell of the 

 Terebratula. 



Fig. 463. The Animal of the 

 Terebratula. 



stomach is sufficiently developed, and the intestine forms 

 around the liver circumvolutions before reaching the pos- 

 terior edge of the base of the abdomen, where it ter- 

 minates. The heart is generally situated above the visceral 

 mass thus formed (Fig. 160), and is composed of an aortic 

 ventricle, and of one or two- auricles, destined to receive the 

 blood from the gills. In general this ventricle is fusiform, 

 and presents a remarkable peculiarity, its cavity being tra- 



