Mr. Robert Gamer's Malacological Notes. 367 



bj Cuvier to distinguish the separate families. They are 

 generally protected by a shell, and arc of course en liaison 

 with the heart, as the latter is, more or less, with the alimen- 

 tary canal ; indeed we should have before observed that in 

 the Lamellibranchiatcs the ventricle is commonly traversed by 

 the rectum, this arrangement being either an advance ujjon 

 the disposition seen in still lower animal forms, where the 

 intestine is enveloped by the general reservoir of the blood, 

 or, as has been thought, due to the young bivalve being the 

 result of the union of twin embryos. It is probable, as may- 

 be traced in their vascular arrangement, that the branchige in 

 mollusks arc normally four in number, as we see them in 

 bivalves and again in Nautilus ; the two of one side, how- 

 ever, are combined into a single one in most Gastropoda, 

 and in some Arav, Anafina, tiolemjja, and other bivalves ; 

 or one only, altogether (homologically duplex however), may 

 exist, as in other Gastropods, its fellow of the opposite side 

 being more or less undeveloped. Are the pair of branchiae 

 found in ihe dibranchiate Cephalopoda the representatives of 

 the four branchia3 of the tetrabranchiate iVaii^zVe^s ? or have we 

 the rudiments of the wanting pair, or simply of the corre- 

 sponding cardiac parts, in the anomalous appendages of the 

 lateral hearts, which, however, are wanting or little developed 

 in Octopus'i The monobranchiate >l/j//y6«a has an aortal appen- 

 dage. Some of the Gastropoda have pulmonary sacs instead 

 of branchiffi, and others {^Ampullaria and perhaps some lit- 

 toral species) have both*. 



The position of the branchias in Patella and Chiton (Cyclo- 

 branchiata) is analogous to that in the bivalves, to which 

 mollusks these Gastropods form the natural transition ; but the 

 ventricle of the heart has not the intimate connexion with the 

 rectum, though both heart and rectum are situated at the 

 posterior extremity of the body in the latter genus. Not so 

 in those allied genera where the branchiae have ascended wholly 

 orpartiallyabove theneck(Scutibranchiata) — Fissurella,Emar- 

 giuula, and Jlaliotis; for here the ventricle and rectum are in 

 union, as in the bivalve. In Jlaliotis and Sigaretus one 

 branchial plume is commonly less than its fellow ; and in 

 Jlaliotis the inequilateral composition of the shell is indicated 

 by the row of foramina. In Calgptraia and its congeners the 

 smaller of the branchiae has disappeared ; and in this last case, 

 probably, the shell is correspondingly the expanded representa- 



* The circumpedal frin^re of Patella has doubtlessi a branchial function ; 

 but we do not deny that the animal, when exposed bv the receding tide, 

 may take air into the suprador>al cavity, thouj^li this rather appRare to 

 be the renal organ. 



