\ K i I : I i 



Ruilula having many longitudinal n.u- ift-rth, tin- n-ntral- 

 narnw. hardly larger than the side teeth, with tin- cusp serrate^ 

 side teeth falcate with the cusp l<uig and serrate, becoming sirup!*- 

 on the outer teetli. 



The genera here assembled agree in the common character of a 

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

 ii la with teeth of the primitive Tectilmmch type found in Aj> : 

 (In-, etc When the anatomy of Ci/fin tlrofml/n. and IV/v//// 

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

 essary. 



Synopsis of Subfamilies and Genem. 

 *Epijiwlinl lobes developed, large. 



Subfamily AKERIN/E (Aceridce Mazzarelli). 



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

 deep sutural slit and wide anal fasciole. Anirual 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.T-: 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.E Pilsbry. 



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

 slit or a po-terior "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, hilolird 

 behind. No epipodial lobes. Dentition unknown. 



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

 ing the suture. Genus Cylindrobulla (see plate t_\ figs. 1'.' 

 20). 



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



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



