258 



ZOOLOQT. 



the preceding class, and is, by some authors, regarded as 

 the type of a separate class \8caphopoda). The sexes of 



Fig. 181.— Development of Bentalhnn. A, morula ; B, trochosphere ; C, annu- 

 lated larva ; D, larva with its rudimentary shell ; z, velum ; a, shell ; E, young much 

 farther advanced, the shell or hody segmented ; d\ rudimentary tentacles ; j, sub- 

 ce.^ophageal nerve-ganglia; //", digestive canal, and liver (/'); the foot protrudes 

 from the shell. All magnified.— After Lacaze-Duthiers. 



Dentalium are distinct. The young is a trochosphere and 

 afterwards becomes segmented, and the univalve 

 shell then appears. (Fig- 182.) 



Order 2. Pteropoda. — In these winged-snails 

 the head is slightly indicated and the eyes are 

 rudimentary ; while they are easily recognized by 

 the large wing-like appendages {epipodiuni), one 

 on each side of the head. The shell is conical 

 or helix-like. The species are hermaijhroditic. 

 C'avolina tridentata Lamarck and Styliola vitrea 

 Verrill (Fig. 183) are pelagic forms, occurring on 

 Fig. Ki.-pen- t]ie high seas, and are occasionally taken with the 



talivm Indiana- , «. ,i „ tit -n n -i 



rmn. Used as tow-net Oil the Southern coast of JNew England. 



shell money. — . .•-n-u-jjii • ? i 



After Stearns. Limacina circtica Fabr. is of the size of, and 

 looks like, a sweet pea, moving up and down in the water. 

 It is common from Labrador to the polar regions. 



