VII MOLLUSC A— SYSTEMATIC REVIEW 5 



= Parmophorus), Pic n roiomaiidcc [Pkurotomaria, ScissurcUa, Pohjtrcmaria), Bcllcro- 

 jjhontidcc (exclusively fossil). 



b. Azygobranchia. — One gill, homologous with the left gill of the Zcvrjo- 

 hranchia. Right auricle ending blindly. Heart perforated by the rectum. Fam. 

 Turbonidcc, rad. oo0.(5.1.5.)0.cc , Trochidce (Fig. 3) Stoviatiidce, Keritopsida!, rad. 

 ool.(2.0.2.)l.oo, marine, Neritidce, rad. ool.(3.1.3.)l.oo (marine, but along the shore 

 able to live out of water), Neritinoe, (marine and fresh-water). The Hydrocoenida, rad. 



ool.(l.l.l.)l.oo, and HcUcinidce, rad. cc 1.(4.1. 4.)1. 00 , have no gills but a lun<r 

 resembling that of the Pulmonata. The HcUcinidce are terrestrial. 



c. Docoglossa. — Heart with one auricle, and not perforated by the rectum. Left 

 kidney shifted to the right side of the pericardium. Visceral dome and shell 

 secondarily symmetrical, the latter usually cup-like. Operculum wantino-. ilarine. 



Fig. 5.— Phorus exutus (after Lankester). «, Proboscidal snout or rostrum ; h, teutaclf ; 

 c, eye; rf, foot; e, inetapodiuin witli operfuluin/. 



1. Left true ctenidium present. Acmacida;, rad. 1.2.(1.0.1.)2.1. ; with numerous 

 accessory gills in the mantle furrow : Scurria ; — without such gills : Acmaca 

 {Tccticra). 



2. True ctenidia altogether wanting, accessory gills very numerous in the mantle 

 furrow.— Fam. Patdlidcc (Fig. 4), rad. 3.1.(2.0.2.)1.3. 



3. Neither ctenidia nor accessory gills found {Lc2)ctidcc), rad. 2.0.1.0.2. 



Sub-Order 2. Monotocardia (Pectinibranchia). 



Heart with one auricle. A single true ctenidium feathered on one side, the point 

 not projecting freely (except in Valvata). Pedal nerve trunks a rare exception, pedal 

 ganglia the rule. Only one kidney. Siphon and penis generally ju'esent. Ejii- 

 podium weakly develojied or wanting. The Monotocardia are very numerous and 

 are chiefly marine. 



a. Architaenioglossa. — Pedal nerve trunks. In Gypraca (and in other forms ?) a 

 rudiment of the right auricle persists. Fam. Cypraeidcx, rad. 3.1.1.1.3, Paludmid,x 

 (fresh-water), Cyclophoridce (terrestrial, pulmonata). 



