vii MOLLUSC A SYSTEMATIC REVIEW 5 



= Par>nophonis), Plev rotomaridce (Pleurotomaria, Stissurella, Polytrcmaria), Bellero- 

 phontidce (exclusively fossil). 



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

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



Turbonidce, rad. a>0. (5.1.5. )0.oo , Trochidce (Fig. 3) St&matiidce, Neritopxidce, rad. 



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

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



ool.(l.l.l.)l.o), and Jfelicinidce, rad. oo 1. (4.1.4.)!. oo , have no gills but a lung 



resembling that of the Pulmonata. The Helidnidce 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 wanting. Marine. 



Fi<~;. 5. Phorus exutus (after Lankester). a, Proboscidal snout or rostrum ; b, tentacle ; 

 . eye ; d, foot ; e, metapodium with operculum /. 



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

 accessory gills in the mantle furrow: Scurria ; without such gills: Acmaea 

 (Tectura). 



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

 furrow. Fam. Patellidce (Fig. 4), rad. 3.1. (2.0.2.)!. 3. 



3. Xeither ctenidia nor accessory gills found (Lcpetidce), 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 present. Epi- 

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

 are chiefly marine. 



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

 rudiment of the right auricle persists. Fam. Cypraeidce, rad. 3.1.1.1.3, Paludinidce 

 (fresh-water), Cydvphoridce, (terrestrial, pulmonate). 



