166 MOLLUSCA. 



tre. The mouth is situate underneath the tentacula. It 

 consists of a large funnel, covered within with soft papillae, 

 destitute of jaws or tongue. The gullet is short, the sto- 

 mach simple, fleshy, and covered with a thick cuticle. The 

 salivary glands are slender and branched, and open into the 

 gullet. The intestine is likewise short, and proceeds di- 

 rectly to the anus. The liver pours the bile into the canal 

 at the pylorus ; and likewise sends out another duct, which 

 opens externally near the anus. The organs of generation 

 are similar to the Doris. The T.fimbria is the type of the 

 genus, a figure of which, with its anatomical details, is given 

 by M. Cuvier, in his Memoire sur le Genre Thetys. 



GENUS VALVATA. In this genus are included several 

 species which resemble in aspect the aquatic pulmoniferous 

 gasteropoda. The branchiae appear in the form of a fea- 

 ther, with a central stem, and a row of compound branches 

 on each side, decreasing in size from the base to the free 

 extremity. This stem issues from the neck near the middle, 

 a short way behind the anterior tentacula. Near this plume, 

 but towards the right side, is a single simple filament, like 

 a tentaculum. The anterior tentacula occupy the usual 

 position, are setaceous, and have the eyes placed at the base 

 behind. The spiral shell is capable of containing the body, 

 and the aperture can be closed by a spirally striated oper- 

 culum attached to the foot. The internal structure is un- 

 known. 



GENUS PATELLA Shell entire. Mouth with tentacula. 

 This genus differs from the others of the order to which it 

 belongs. The back is covered by a conical shell, within 

 the cavity of which the animal is capable of withdrawing 

 itself. The cloak is large, covering both the head and foot. 

 It is united with the shell along its superior margin. The 



