164 SYSTEMATIC ARRANGEMENT 



outside with a condyle, to which corresponds the trapezoidal cavity 

 of the apical minute bone ; other teeth equal in shape ; hook ovate- 

 lanceolate, serrulated. — Loven. 



4. Hemitoma. 



Shell conical, compressed, cancellated or tuberculated ; vertex 

 inclined towards the posterior margin ; aperture large, with fold on 

 the front edge. 



1 . H. emarginata. 



2. H. octoradiata. 



5. Clypidina. 



Shell ovate, conical, radiately ribbed ; vertex acute, central, not 

 recurved ; aperture crenulated on the edge ; muscular scar fungi- 

 form ; anal groove and emargination very small, indistinct. 



1. C. notata. 



c. Vent anterior 1 Shell none. 



6. Deridobranchus. 



" Body like an Emarginula, without any shell. Front of the mantle 

 plaited, covering two pectinated gills. Upper tentacles none, lower 

 two. Eyes at the base of the lower tentacles." 



D. Argus, Ehr. Orbicular, orange, very finely cinnabar-dotted ; 

 the larger dots with an orange ring, and a transverse, curved, hyaline 

 band. Red Sea. 



d. Vent dorsal, subapical. Mantle and shell with a slit or perfo- 

 ration near the tip. 



f Shell exposed. Anal slit subapical, guarded by a shelly channel 



within. 



7. Puncturella. 



Shell conical, cancellated, radiately ribbed ; apex elevated, recurved, 

 obliquely spiral ; a linear perforation in front of the apex in the 

 line of an elevated rib ; aperture crenulated on the edge ; cavity 

 with a vaulted plate over the anterior perforation ; muscular scar 

 crescentic. Head proboscis-shaped ; tentacles subulate ; eyes on 

 protuberances on the outer base ; mantle-edge simple, produced 

 into a tube emitted through the subapical slit ; branchial plumes 

 two ; anal siphon prominent ; lateral fringe of cirrhi interrupted 

 behind. 



1. P. Noachina, Forbes $■ Hanley, B. M. t. B.B. f. 4, 5, 6. 



