VI 



III. Radula with few teeth in a row, or none. No pleuropodial 



lobes. 



a. Shell oval, solid, mottled and variegated (except in a few 

 deep water forms), spire umbilicated or concealed ; rad- 

 ula formula 1.2.1.2.1, the rachidian tooth largest; 3 

 corneous, dumb-bell shaped stomach-plates, 



aa. Shell small, unicolored ; no teeth ; 3 flat, oval, stomach- 

 plates with coarsely tuberculate inner faces, 



TornatinidcB, Vol. XV, p. 180. 



IV. Radula with few teeth in a row, or none ; pleuropodial lobes 



well-developed or very large (? except in Ringiculidce) . 



shell often concealed and partly uncoiled or degenerate. 



a. Shell obese, ovate, small, with thick outer lip and plicate 



columella (pleuropodial lobes wanting?), 



Ringiculidce, Vol. XV, p. 393. 



aa. Shell few-whorled or degenerate, if spiral the aperture very 

 large, as long as the shell. Pleuropodial lobes large. 

 b. Shell external to mantle, 



Scaphandridce, Vol. XV, p. 242. 



bb. Shell wholly concealed in the mantle ; no rachid- 

 ian teeth. 



c. Radula present ; shell spiral, more or less 



open, wholly calcified; pleuropodia of mod- 



erate size, Philinidce, p. 1. 



cc. Radula present ; shell reduced to a minute 



nautiloid calcareous spire and a large, 



open cuticular body- whorl ; pleuropodia 



extremely large, Gastro2)teridce, p. 39. 



ccc. No teeth ; shell a flattened open spiral ; 



head and back shields subequal, the pleu- 



ropodia reflexed partly over them, 



Aglajidce, p. 43. 



The accompanying diagram expresses the general relationships of 

 the families of Cephalaspidea, as understood by the writer. 



