( 66 ) (Pectlnibranchi. Trochoida.) 



k 



J5 



K 

 « 

 s. 



«£> 



S 



t 



2 



/f. Cyclostoma, Lam. 



A vascular net-work 

 on the partitions of the 

 pectoral cavity, instead 

 of branchiae ; respira- 

 tory cavity communi- 

 cating with the exte- 

 rior air by a lateral 

 cleft. 



g. Helicina, Lam. (1) 

 Head proboscidi- 



form, bilabiate ; respi- 

 ratory cavity as in Cy- 

 clostoma. 



h. Valvata, Muller. (2) 

 With branchiae. 



t. Paludina, Lam. (3) 



With branchiae ; a 

 very short trunk. PI. 

 14, fig. 19. PI. 17, fig. 

 2. 



/. Monodonta, Lam. 



Animal more orrta- 

 namented, generally 

 with three filaments 

 on each side as long 

 as the tentacula. 



2 Tentacula terminated 

 by blunt tubercles. 



Eyes on two tubercles 

 near the base of the ten- 

 tacula. 



2 Filiform tentacula. 



Eyes at the outer base. 



2 Slim tentacula. 



2 Pointed tentacula. 



Eyes at the superior 

 base* 



Eyes at the outer base. 



V 



2, Trochus. Lin. 



Mouth of the shell an- Three filaments at 

 gular, more or less quad- each edge of the man- 

 rangular, oblique to the tie, or appendages to 

 axis. the foot. PI. 17, fig. 3, 



4, 12*, 13. 



a. Trochus. 



b. Solarium. 



(1) M. Blainville is convinced that this is the place of the Helicina ; but M. de 

 Ferussac says that it has a collar, with the respiratory hole pierced to the left. 



(2) In the V. cristata the branchiae, formed like a feather, proceed from under- 

 neath the mantle, and float beyond it with a vibratory motion when the animal 

 wishes to breathe ; on the right side of the body is a filament resembling a third 

 tentaculum. 



(3) The female of the P. vivipara produces living young, which are found in her 

 oviductus, in the spring, in all the stages of developement. Spallanzani asserts that 

 these young separated at the moment of their birth, and nourished apart, repro- 

 duce without fecundation like those of the Vine-fretter. The P. cristata one of 

 the small species found in salt water ponds, and described by M. Beudant, moves 

 its tentacula incessantly as oars when it sails on the surface of the water. 



