190 MOLLUSCA. 



municates with it by many orifices. The intestine passes 

 down to the hinge, and then turns to the right side and 

 terminates between the two mantle-lobes. No trace of a 

 salivary gland v/as found. 



The generation of Terebratula is that of the ordinary 

 Bivalves. In two of the larger specimens the ova had in- 

 sinuated themselves between the layers of the mantle, and 

 partly surrounded the branchial vessels. When so far ad- 

 vanced they obscure the organization of the mantle which 

 adapts it for respiration : this organization is consequently 

 most satisfactorily observed in very young individuals. 



The peculiar internal testaceous apparatus or loop con- 

 nected w T ith the hinge and supporting the arms, possesses 

 some elasticity, and when acted on by the muscles, becomes 

 in its reflected part sufficiently convex to press upon the 

 perforated valve and separate it slightly from the opposite 

 one ; thus compensating for the absence of the thick arms 

 of Lingula, which, in their protrusion, push open the valves, 

 and also for that of the elastic fibres, constituting the liga- 

 ment of ordinary Bivalves. 



In the Orbicula lamellosa the same intelligent observer 

 traced along the whole circumference of the valves, shining 

 cilia projecting for an extent varying from two to four lines: 

 they are consequently much longer than in Terebratula and 

 in Lingula anatina, and are rather longer than in Lingula 

 Audebardii, Brod. On examination under a higher power 

 they are observed to be beset with smaller setae, which pro- 

 bably give them greater power in determining the respira- 

 tory currents. The mantle is similarly vascular to that of 

 Terebratula, there being, in the upper lobe, four principal 

 trunks (comparatively, however, much shorter than in that 

 genus) ; and two in the lower. These trunks terminate in 



