GASTEROPODA. 



97 



Shell, bent once upon itself; the two straight portions in contact. 

 Distr., 7 sp. Neocomiau — chalk. Brit. France. 



Baculites, Lamarck. 

 Etym., bacillus, a staff. 

 Ex., B. anccps. PI. III., fig. 13. 



Shell, straight, elongated ; aperture guarded by a dorsal process. 

 List)-., 11 sp. Neocomian — chalk. Europe, S. America (Chile). 

 Baculina, D'Orb. B. Rouyana. Neoc, France. Sutures not foliated. 

 The chalk of Normandy has received the name of baculite limestone, from 

 the abundance of this fossil. 



CLASS II. GASTEROPODA. 



The gasteropods, including land-snails, sea-snails, whelks, limpets, and the 

 like, are the types of the mollusca ; that is to say, they present all the leading 

 features of molluscous organization in the most prominent degree, and make 

 less approach to the appearance and condition of fishes than the cephalopods, 

 and less to the crustaceans and zoophytes than the bivalves. 



Their ordinary and characteristic mode of locomotion is exemplified by the 

 common garden-snail, which creeps by the successive expansion and contraction 

 of its broad muscidar foot. These muscular movements may be seen foUownig 

 each other in rapid waves when a snail is climbing a pane of glass. 



The nucleohranches are "aberrant" gasteropods, having the foot thin and 

 vertical ; they swim near the sm-face of the sea, in a reversed position, or 

 adhere to floating sea-weed. 



-^ 



A nucleobrmiche.* 

 •e nearly all nns^Tiimetrical, the body being coiled up 



The, gasteropods 

 spirally, and the respiratory organs of the left side being usuaUy atrophied. 

 In c/ilton and dentalium the Iranchue and reproductive organs are repeated 

 on each side. 



* Fig. 5!). Carinaria cymbium, 

 boscis; /, tentacles, b, branchise; . 



L. sp. (after Blainville), Mediterranean ; p, pro- 

 .■, shell ; /, foot ; d, disk. 



