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 fy Ilanley, B. M. t. B.B. f. 4, 5, 6. 



