282 SCISSURELLIDiE. 



Family VI. SCISSURFLLID.E, Gray. 



Body more globular than conical, spiral : tentacles long, 

 ciliated: eyes at the outer bases of the tentacles: foot furnished 

 with pointed lappets on each side, besides tentacular append- 

 ages. 



Shell corresponding in shape Tsdth the body or animal, 

 white, nacreous, and thin : month somewhat angulated : outer 

 li}) vertically fissured at the edge, or having an orifice a little 

 behind it : iimbilicus narrow, but conspicuous : operculum 

 horny, thin, circular, and multispiral, with a central nucleus. 



The recent genera [Scissurella and Schismope) which 

 constitute this family have their analogues in the fossil 

 genera [Pleurotomaria and Trochotoma) , if indeed the 

 two last named are not the same as the two first. 

 Living species of Pleurotomaria have been lately de- 

 scribed and figured in the ^ Joui'nal de Conchyliologie ' ; 

 they do not seem to diflPer from those of Scissurella^ 

 except in their greater size and coloured markings. 

 The nacreous inner layer of S. crispata is very evident 

 when the shell is broken or has been accidentally exfo- 

 liated. The absence of nacre in Scissurella was regarded 

 by Fischer and Bernardi as a distinctive character of 

 Pleurotomaria. The slit or fissure probably serves the 

 same purpose as that of Emarginula, Puncturella, or 

 Fissurella, and the orifices in Haliotis, by admitting 

 water to the branchial cavity. The conformation and 

 habits of the animal may require this additional pro- 

 vision for aerating the gills. In most other respects 

 the Scissurellidce resemble the Trochida ; in every one 

 of them the foot lias tentacular appendages, the shell is 

 spirally conical, and the operculum is concentrically 

 spiral. Too little, however, is known with regard to 

 the animals of the present family to pursue the compa- 

 rison to anything like a complete or satisfactory extent. 



