BRODERIPIA-SCISSURELLA. 49 



Family SCISSURELLID.E. 



Shell minute, unicolored, umbilicated, turbinate or depressed, few- 

 whorled, thin, with a thin layer of pearl inside ; aperture oval, outer 

 superior lip with a foramen or slit as in Pleurotomaria, and with a 

 differently sculptured band or anal fasciole encircling the whorls 

 Operculum circular, corneous, thin, multispiral, with central nucleus. 



Animal with a rather long rostrum, long, ciliated tentacles, the 

 eyes at their outer bases ; foot rather narrow ; epipodium bearing 4 

 ciliated cirri on each side. Radula as in Trochidse; tooth formula 

 oo-l (4-1-4) l*oo . Central and lateral teeth with large expanded 

 basal plates and finely denticulate recurved cusps. Uncini very 

 numerous, narrow, with serrate cusps (pi. 50, fig. 18). 



A group of very small shells, most of them living in deep water. 

 The fossil (tertiary) species number about as many as the recent. 

 The shell has a considerable resemblance to that of Pleurotomaria, 

 but the dentition and external anatomy of the animal is decidedly 

 nearer Trochidce. 



Genus SCISSURELLA d'Orbigny. 



Shell with an open anal slit, extending backward from the peri- 

 stome ; slit fasciole extending nearly to the apex. Type, S. laevigata 

 Orb. 



Genus SCHISOMOPE Jeffreys. 



Anal fissure closed, forming a foramen in the outer wall of 

 aperture; slit fasciole shorter, not over \\ whorls in length. Type, 

 S. cingulata Costa. 



Genus SCISSURELLA Orbigny, 1823. 



Scissurella Orb., Mem. Soc. d'Hist. Nat. de Paris, i, p. 340, 1823. 

 — Anatomus H. & A. Adams, Genera, i, p. 439 not Anatomus Mont- 

 fort, 1810. — Schizotrochus Monterosato, JSTom. Gen. e Spec, p. 39, 

 1884, type, S. crispata Flem. 



The type of Scisurella is S. laevigata Orb., not S. elegans Orb., 

 which is the last species in Orbigny's original monograph. Orbigny 

 men iions a deep slit, but not a foramen in the outer lip. There is 

 considerable variation in contour among the species, and this may 

 sometime be utilized to break the genus into sections ; meantime, as 

 I do not see any characters of much value, I consider Schizotrochus 

 of Monterosato a synomym. 

 4 



