164 MOLLUSC A. 



GENUS TRITOXIA. Branchiae destitute of basilar sheaths. 

 The branchiae are in the form of plumes, or imbricated pro- 

 ductions, placed in a row on each side the back. The ten- 

 tacula, which are partially retractile, have a sheath at the 

 base. In some of the species there are indications of eyes. 

 The mouth consists of two lips, which are placed longitudi- 

 nally, and open into a short canal. The jaws consist of two 

 corneous plates, united at the upper dorsal edge, slightly 

 arched, and meeting at their upper margin, for the purpose 

 of cutting. Within these is the tongue, which differs re- 

 markably from the same member in the doris. In the lat- 

 ter, the spines with which it is beset are reflected, and draw 

 the food to the gullet, while in the former, the spines are 

 deflected, and serve to keep the food within the reach of 

 the jaws. The tongue of the doris, therefore, serves for 

 deglutition, that of the tritonia for mastication. M. Cuvier 

 describes the functions of both as similar. The salivary 

 glands are placed on each side the gullet, and empty their 

 contents behind the jaws. The gullet has a few longitudi- 

 nal folds ; the stomach is simple, scarcely differing from the 

 gullet ; and the intestine proceeds almost directly to the 

 anus, situate on the right side. The liver is small, and situ- 

 ate behind, enveloping the stomach, and intimately united 

 with the ovarium. The organs of generation exhibit no- 

 thing remarkable. The pedunculated vesicle has a simple 

 canal. The external opening of the organs of generation 

 is situate a little before and beneath the anus. The T. 

 Hombergii arborescens, pinnati/ida, and bifida, are exam- 

 ples of British species. 



GENUS SCYLLEA. Branchiae seated dorsally on the fins. 

 Tentacula two. On each side of the back are two mem- 

 branaceous expansions, and one on the tail, supporting on 



