vlr. J. E. Gray on Prof. LoveVs Homologies of Mollusca. 217 



distant part of the mantle. In the spiral gasteropods tne water 

 enters by the front edge of the mantle, and is ejected at the 

 hinder edge ; the place where it is ejected is generally marked 

 by a tooth or ridge on the hinder part of the inner lip of the 

 shell, forming a canal with the outer lip ; and sometimes the place 

 of exit is marked by a more or less elongated canal on the shell, 

 as in the genera Ovulo, Cypraa, Cassis, &c. From the examina- 

 tion which I have made of the animal of Pleurotoma and Man- 

 gelia, I much doubt if this slit in the lip of the shell is used 

 like the excrctorial siphon of the bivalve mollusca, for the ex- 

 pulsion of the water which has been used in respiration. It 

 may be used for the exit of the rejectamenta from the intestine, 

 like the perforation in the shell of Dentalium, Fissurella and 

 Haliotis, and the notch in the front of the shell in Emarginula 

 and Scutum. 



Thirdly, Professor Loven regards " the cardinal teeth of the 

 bivalves, and the apophyses of the hinge of Brachiopods, as 

 probably homologous with the septa that separate the chamber 

 of Xautili and the solid shelly matter which fills up the cavity of 

 the shell of Magillus." There is no doubt of the similarity of 

 these parts, if we are merely to regard them as additional layers 

 of shelly matter added to the shell; but if we are to consider 

 their use in the oeconomy of the animal, I cannot see any simi- 

 larity between the cardinal teeth of the bivalves, and the shelly 

 layers which diminish the size of the cavity of the shell. The 

 former are used to keep the two valves of the shell in their pro- 

 per relation to each other; and the latter, whether it forms 

 a solid body as in the Magillus, or leaves certain spaces be- 

 tween each series of plates as in the Xautilus, is used for the 

 purpose of letting the shell keep its proper relation with the 

 body and head of the animal. The cardinal teeth of the bivalve 

 appear to be the real homologue with the lobes on the opercu- 

 lum of Neritida, which keep the operculum in its proper relation 

 with the shelly valve, and are analogous to the teeth, folds or 

 ridges in the mouth, the grooves in the throat, and the folds in 

 the pillar of certain spiral shells, which appear to be destined to 

 keep the animal in its proper position in the cavity of the shell ; 

 and, like the teeth of the hinge, are formed by folds or loops of 

 the mantle. It may be observed that many shells like the Os- 

 trece and Mytili, which have no true cardinal teeth, have more 

 or less large eminences near the hinge or fold in the exterior 

 margin of the shell, which serve the same purpose as the cardinal 

 teeth in keeping the valves in their relative situation with regard 

 to each other. 



