MOLLUSCA. 189 
TEREBRATULA. Valves unequal, the peduncle passing 
through an aperture in the largest valve. 
The following interesting information, from the dissec- 
tions of Mr. Owen, will be read with pleasure by the student 
of the anatomy and physiology of the mollusca. 
The mantle adheres very closely to the valves: the lobe 
which corresponds to the perforated valve is traversed longi- 
tudinally by four large vessels ; the opposite lobe is simi- 
larly traversed by two such vessels. Its margins are thick- 
ened, not as in the Lamillibranchiate Bivalves from con- 
traction, but owing to a peculiar structure connected with 
respiration. They are puckered at regular distances, the 
puckerings being apparently caused by the insertion of de- 
licate czlia, which pass as far within the mantle as they pro- 
ject out of it, but which are so minute as to be observable 
only by means ofa lens. In the interspaces of the cilia the 
margin of the mantle is minutely fringed, and within the 
fringe is a canal, which extends along the whole circumfer- 
ence. From this canal the large vessels of the mantle lobes 
take their origin: they may be regarded as the branchial 
veins conveying the aerated blood to the two hearts, which 
are situated exterior to the liver, and just within the origin 
of the internal calcareous loop: they are accompanied in 
their course by much smaller vessels, probably the branchial 
arteries. Such is apparently the system of respiration in 
Terebratula. , 
The viscera occupy a very small space near the hinge. 
The alimentary canal commences by a small puckered 
mouth, situated immediately between the folded extremi- 
ties of the arms. It passes backwards, and expands into a 
membranous stomach, surrounded by the liver, a bulky gland 
of a green colour and minute follicular texture, which com- 
