ANATOMY OF THE LAMELLIBRANCHIATA. 165 



they are long and volute. They are large in the Tellina and 

 similar genera; small in Modiola, Mya, Psammobia, &c. 

 When lips are developed the tentacles are small. These are 

 of a fringed appearance in Pecten, Spondylus, &c, more foli- 

 ated in Chama. 1 The mouth is small in Venus, &c, 

 larger in several of the Monomyaria. The oesophagus, gene- 

 rally very short, is however occasionally pretty long, as in the 

 Pholas. Home describes salivary glands in the Teredo, but 

 these I have not been able to find ; and Poli, bodies which 

 he supposes to be such in the Pinna. The stomach is 

 always in the centre of the liver, and the bile ducts enter it 

 by one or more orifices. Into the stomach projects the 

 extremity of a lengthened cartilage, the " crystalline style" 

 of Poli. The other extremity has been described as going to 

 the foot, and adding to the elasticity of that organ. This 

 body is of various shapes, and has at its superior extremity 

 a cartilaginous membrane, the " tricuspid body" of Poli. 

 This lies at the inferior surface of the stomach, and its extre- 

 mities enter the bile ducts. The crystalline style is wanting 

 when the foot is small; the membrane is always present. 

 The former is evidently analogous to the tongue of the Pa- 

 tella and other cephalous Mollusca ; it is secreted from be- 

 hind and comes forward into the stomach ; the membrane at 

 its extremity is analogous to the membrane always found in 

 a similar situation at the end of the tongue in other Mollusca. 

 The apparatus of mastication in the Gasteropoda is then in 

 the Lamellibranchiata partly subservient to digestion, but 

 has also another use assigned to it — the giving elasticity 

 to the foot, or, in the Anomia, where its extremity is seen in 

 the mantle, the preserving in its situation the free extre- 

 mity of the left lobe of the latter part. 



These organs have been supposed by Poli to regulate the 

 flow of bile; which appears probable. By Cams 2 they are 

 imagined to be concerned in the function of generation, which 

 supposition is not warranted by the facts ; but, on the con- 

 trary, there are grounds on which we may infer that it is un- 

 likely. The duodenum or first part of the intestine is wider 

 than the remainder and is by some called a second stomach. 

 It sometimes originates from the true stomach distinct from 

 the style, as in Mactra, Pholas, 2 some species of Solen, &c. 

 Sometimes the style lies in a groove of the duodenum, which 



1 Poli. 2 Lehrbuch, v. 2. 



3 The digestive system of the Teredo only differs from that of the Pholas 

 in its greater length. 



Vol. III.— No. 28. n. s. s 



