Mr. A. Hancock on the Animal of Chamostrea albida. Ill 



nicates with the exhalant siphon, the stream will pass readily out 

 of the animal. 



The minute structure of the rudimentary gill is precisely 

 similar to that of the laminse forming the gill-plate ; and the 

 plicae of the former are continuous with those of the latter. The 

 sedimentary matters will therefore, in all probability, pass from 

 one to the other, and be collected, as usual, along the free 

 anterior margin (fig. 1 /, /) of the gill, which margin is provided 

 with an ample groove (fig. 7 a) for the purpose, formed by the 

 projection of the plicse {b, b) of both sides; and in this manner 

 the nutriment will be conducted to the mouth. 



The water strained through the rudimentary gill will pass 

 along the dorsal or posterior margin external to the membrane 

 which defines the great channel at the root of the gill-plate, 

 and thus reach the exhalant siphon, which is provided at its 

 internal orifice with two lateral membranous processes (PI. III. 

 fig. 3 o) ; these are united below, partially separating the two 

 tubes; above each forms an angulated lobe which projects for- 

 ward as far as the lower extremity of the rudimentary gill, and 

 is undoubtedly for the purpose of guiding the excurrent branchial 

 streams to the siphonal outlet. This membranous process is 

 apparently the rudiment of the septum which completes the 

 separation of the tubes in the Pholades, and in several other 

 Lamellibranchs. 



The alimentary system presents nothing very peculiar. The 

 oesophagus is well defined, moderately long, and ascends a little 

 as it passes backwards to reach the upper portion of the stomach, 

 which is ii-regularly rounded; below it becomes suddenly con- 

 stricted, and is prolonged almost to the lower extremity of the 

 body, where it terminates in a blind sac. In this elongated 

 portion there is a narrow plait of the lining membrane extending 

 near its whole length, and giving off on either side short, alter- 

 nate branches. The biliary ducts are seven or eight in number ; 

 five or six of these enter the superior portion of the stomach, — two 

 the inferior prolongation ; but these latter were not very distinct. 

 I did not succeed in tracing the whole of the intestine ; but it 

 appears to me to leave the upper portion of the gastric organ 

 behind, just above the commencement of the inferior prolonga- 

 tion ; and passing a little upwards and backwards, curves round 

 the upper extremity of the posterior adductor, and then coursing 

 along its external margin, terminates below it in a short, free, 

 tubular anus within the base of the exhalant siphon : the margin 

 of the anus is entire. Thus it would appear that the intestine 

 is shorter than usual. It is possible, however, that the above 

 description may, on further examination, require modification ; 



