AKERID^E. 351 



Radula having many longitudinal rows of teeth, the centrals 

 narrow, hardly larger than the side teeth, with the cusp serrate ,- 

 side teeth falcate with the cusp long and serrate, becoming simple 

 on the outer teeth. 



The genera here assembled agree in the common character of a 

 light-colored, thin shell, and (as far as known) a multidentate rad- 

 ula with teeth of the primitive Tectibranch type found in Aplysii- 

 dce, etc- When the anatomy of Cylindrobulla and Volvatella is 

 better known, a division into two or three families may become nec- 

 essary. 



Synopsis of Subfamilies and Genera. 

 ^Epipodial lobes developed, large. 



Subfamily AKERIN^E (Aceridce Mazzarelli). 



Shell fragile, elastic, with entirely exposed, nearly level spire,, 

 deep sutural slit and wide anal fascicle. Animal with long narrow 

 head disk, large epipodial lobes reflexed over the shell, and many 

 cartilaginous stomach plates. 



Contains the single genus Akera (see pi. 42, figs. 11-18). 



Subfamily HAMINEIN^K Pilsbry. 



Shell brittle, with concealed spire; a posterior sinus, but no 

 sutural slit or anal fasciole ; the interior not wholly visible from 

 base. Animal with a quadrate head disk, bilobed behind ; epipo- 

 dial lobes large, reflexed over the shell. Principal stomach plates 

 three. 



Contains the single genus Haminea (see pi. 40, 41). 



* * No epipodial lobes. 



Subfamily VOLVATELLIN^: Pilsbry. 



Shell fragile and elastic, with concealed spire, and either a sutural 

 slit or a posterior "spout"; no distinct anal fasciole; aperture 

 very narrow above, effuse and open below, showing the whole 

 interior from the base. Animal with a quadrate head disk, bilobed 

 behind. No epipodial lobes. Dentition unknown. 



a. Shell cylindrical, the aperture with a deep narrow slit follow- 

 ing the suture. Genus Cylindrobulla (see plate 42, figs. 19, 

 20). 



b. Shell swollen, contracted at vertex into an erect " spout " ; no 



sutural slit. Genus Volvatella (see pi. 42, figs. 21-23). 



