NATURAL CLASSIFICATION OF THE GASTEROPODA. 243 



able to Scutus or ParmopTiorus, and Dentalium to Fissurella ; 

 while the further progress of shell-development is to be traced 

 through Teinotis, Raliotis, Scissurella, Trochus, Turbo, JVerita, and 

 JVeritina, winding up with the pulmoniferous genera Helicina, 

 Proserpina, and Ceres. 



If all the genera given by Dr. Gray with Helicina as OlygyradaB 

 really exhibit the raphidoglossal type of dentition, this group will 

 become of more importance than has hitherto been supposed. 



Classification of the Gasteropoda (continued). 



Division II. DICECIA (sexes distinct). 



Subdivision I. Lingual membrane unarmed, or with pleural teeth only. 



Order I. Proboscis lengthy and completely retractile, or shorter and not com- 

 pletely retractile in the aberrant family of lanthinida. 



(a) Both rachis and pleura; unarmed ( Pyramidellidee and 



| Canccl/ariidcs. 



(b) Pleura represented by a single / curVed * simple ... Pleurotomida. 



series of teeth on each side 1 straight, \ « lm pk ••• ^cusida. 



\ & ' [barbed... Comdce. 

 ( Outer teeth with additional 1 7 --i a. 



(c) Dentition in the form ' cusps j Solamdtsf. 



of a double pavement, j All the teeth simple and \ Scalariidcs. 

 { uncinate ) Ianthinidce. 



Subdivision II. Litigual membrane strap- or ribbon-like. 



Order I. Proboscidifera. Proboscis lengthy, retractile ; ear-sacs with 



otoliths. 



Suborder 1. Ortiiodonta. Dental processes in general pointing directly back- 

 wards from or from near the posterior border of the basal plates. 



lingual dentition uniserial (rachidian) Volutidcs. 



( Rachis ( .„, . 



and I Dental processes / Stra P short Mitride. 



pleura <( numerous, small. ] Strap long I tee ? 1 short Fasciolarada. 



comb- -r. . , } \ b L teeth long Fusidas. 



ingual like. ( Venta[ processes few and large Turbinellidce. 



lilt }on •{ (Uncinus wit] an additional internal cusp Buccinidcs 



Pleura3 1 — f ( Muricida 



unci- 



nate. 



I I 1UIVI CVlUi 



i Uncinus simple. Cusps large and few -j Olividcs. 



Rachis armed. 1 [ Harpada. 



(_ Cusps small and numerous. Turritidce. . , 

 Uncinus foliated. Rachis unarmed ColumbelJ ,lct(S ' 



* For figures of the different forms of dentition here referred to ' see m ^ 

 paper "On the Homologies of the Dental Plates and Teeth of Prob /0sddiferous 

 Gasteropoda," in Ann. and Mag. Nat, Hist. 1869, iii. pp. 113-116'' pL xiii ' 



t The ear-sacs in this family alone have otoconia ; all the 0' thers have sin S le 

 spherical otoliths. 



19* 



