NATURAL CLASSIFICATION OP THE GASTEROPODA. 213 



able to Scutus or PartnopJwrus, and Dentalium to Fissurella; 

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

 through Temotis, Haliotis, Scissurella, Trochus, Turbo, Nerita, and 

 Neritina, winding up with the pulmoniferous genera Helicina, 

 Proserpina, and Ceres. 



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

 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. DIGECIA (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 Ianthinida. 



(«) Both rachis and pW unarmed (££S ^ 



/7S -m > j , -i /'curved*, simple ... Ptcurotomidcs. 



(b) Pleura represented by a single I , .* , AamSm 



series of teeth on each side | straight, j ^J^ ' ; ; ^^ ' 



/'Outer teeth with additional \ e r ari J + 



(c) Dentition in the form J cusps j 



of a double pavement. ] All the teeth simple and 1 Scalariidce. 

 ^ uncinate j Ianthinidce. 



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



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

 otoliths. 



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

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



(a) Lingual dentition uniserial (rachidian) Volutidcs. 



f ^f S fTW,.i™™ a f ^rap short, .... Jflfrtfe 



(6) Lingual 



oiiu i "^«"i»vn«»ra i f teeth 

 pleura i numerous, small. j Strap long j ^^ loQg M ^ ^ 



c ?^ ' Dental processes few and large Turbinellidcs. 



dentition ■{ f Uncinus witl an additional internal cusp Buccinidce. 



triserial. 



f Muricidce. 



u . -j Uncinus simple. I Cusps large and few \ Olividts. 



un , C I Eachis armed. 1 I Harpada?. 



n I Cusps small and numerous. Turritidce. 

 1 Uncinus foliated. Eachis unarmed Columbelli 



* For figures of the different forms of dentition here referred to, see my 

 paper "On the Homologies of the Dental Plates and Teeth of Proboscidiferous 

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



t The ear-sacs in this family alone have otoconia ; all the others have single 

 spherical otoliths. 



19* 



