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 was 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 with 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 3 
- Yr 
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 4 
trunks (comparatively, however, much shorter than in that i 
genus); and two in the lower. These trunks terminate in — 
