ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA l6l 



dorsal edge, and a deep thin crest surmounts the outer whorl, and 

 is generally broken in several places. The surface of the shell is 

 marked by delicate transverse striations. 



The outer fourth of the outer whorl of the shell is occupied by the 

 mantle, the rest of the spire containing the viscera. 



When protruded, the body of the animal is as large as the shell 

 and appears trifid ; the large head forming the anterior division, the 

 " fin " the middle, and the " tail," with its operculum, the posterior 

 division. 



The head is large and subcylindrical. Its anterior extremity is 

 formed by a circular lip surrounding the mouth. The eyes are placed 

 far back, and the longish conical tentacles proceed from the anterior 

 part of their base. 



The fin or " propodium " {pp) is flattened and fan-shaped ; its edge 

 is provided with many long and delicate hairs, and its surface is 

 covered with little asperities. Just below its point of attachment, 

 the posterior edge of the propodium carries a cup-shaped disc {ms), 

 also fringed with long hairs. This is commonly called the " sucker," 

 and has no representative in Firolo'ides. It may be called the 

 mesopodium. 



The " tail " or metapodium^ (jnt) is subcylindrical at its base, but 

 becomes flattened and acuminated inferiorly. The elongated lan- 

 ceolate transparent operculum is fixed upon its posterior surface. 



The animal moves by the vigorous flapping of its fin. When it with- 

 draws within its shell the head is just retracted, then the fin is folded 

 in, and finally, the tail with its operculum covers up the whole. 



The male is distinguished from the female by the presence of a 

 peculiar leaf-like penis (j>), which is attached upon the right side of 

 the body just above where it divides into the three portions of the 

 foot, fig. I. 



The Alimentary Canal commences above an oval buccal mass, 

 widens gradually into the stomach, then narrows again and opens 

 into a quadrangular sac, which communicates with the liver. From 

 the anterior and upper part of this sac the rectum is continued and 

 runs forward to the upper and dorsal part of the branchial cavity, in 

 which it terminates by a tubular anus. 



The mechanism of the tongue exactly resembles that of Firoloides. 

 Two long cylindrical salivary glands (/) open into the anterior part of 

 the oesophagus. They are simple csca lined by a thick epithelium. 



The Liver (/, fig. 3) is a wide conical sac with sacculated and 



^ That this is the same organ as the metapodium of Firoloides, will be obvious upon com- 

 paring the different forms which it assumes in Carinaria, Carinaroides, and Firola. 

 VOL. I M 



