198 SYSTEMATIC ARRANGEMENT 



Central tooth of Hydatina Physis wanting ; lateral teeth about 

 thirteen, somewhat equal, thick, hooked, reduced in front and at the 

 base; marginal teeth 4 • 5, unequal (fig. 112). — Lovin. 



Fig. 112.— Teeth of Hydatina Physis. 



The genus Atlas, Lesueur, has been referred to this family. It 

 is said to be the larva of Siphunculus. See J. Miiller, Entwick. der 

 Echinod. 36, and Busch, in Arch. Naturg. 1854, 333. 



b. Tentacles slit externally, ear-like, separate. Head produced. 

 Teeth in very numerous longitudinal series, forming angular 

 cross lines, all similar (p. 191). 



■f Shell internal or none (p. 201). 



Fam. VI. APLYSIAD^E. 



Shell internal, rudimentary ; nucleus globular, spiral. Teeth 

 in many longitudinal series; central 1, distinct; lateral numerous, 

 similar. Tentacula separate, ear-like. 



* Sides of foot dilated, covering the back, not expanded for swim- 

 ming. Shell hard, calcareous, covered by the mantle. 



1. DoLABELXA. 



Animal elongate, obliquely truncated behind ; sides of foot in- 

 flexed. Shell calcareous, triangular, convex ; apex callous. Perios- 

 traca hard. 



f Body warty. Shell broad. 



1. D. callosa, t. 137. f. 2. D. Rumphii, t. 134. f. 1, t. 135. 



2. D. ?, t. 133. 



3. D. 1, n. s., t. 207. f. 2. Ceylon. 



ft Body smooth. Shell broad. 



4. D. ecaudata, t. 136. f. 2. 



5. D. Tongensis (Aplysia de Tonga), t. 137. f. 1. 



fff Body and shell elongate. 



6. D. temnida, t. 136. f. 1, t. 270. f. 1. 



