1 86 



THE GASTROPODA 



transformed into a branchia. Genera Ancylus, Geoffroy ; no pulmonary 

 cavity ; animal dextral or sinistral ; visceral commissure shortened ; shell 

 without internal septum ; British (Fig. 176). Latia, Gray ; a pulmonary 

 cavity ; visceral commissure long ; shell witli a posterior internal septum ; 

 from New Zealand. Gundlachia, Pfeiffer. FAMILY 11. PHYSIDAE, Dall. 

 Visceral mass and shell sinistrally coiled ; shell thin, with a narrow 

 aperture ; tentacles cylindrical ; no inferior pallial lobe. Genera 



Physa, Draparnaud ; shell oval, 

 partly covered by the edges of the 

 mantle, which are divided into 

 angular tags ; British. Aplexa, 

 Fleming ; shell with a pointed 

 spire ; edges of the mantle not 



n/rvi 



divided and very slightly re- 

 flected over the shell ; British. 



FIG. 175. 



Lillians talmlatus, ventral aspect. 

 lir, pallial extrapuliiionary jjill ' co, 

 heart; o, mouth; p, loot; j*t, mantl** ; 

 pns, pnemnostoine ; \# t tentacle. 



Fio. 17f>. 



A nnihts flurintilis, dorsal 

 view. To the left, the head 

 with the two cephalic ten- 

 tacles. (From Lankester, after 

 Reeve.) 



SUB-ORDER 2. STYLOMMATOPHORA. 



Pulmonata with two pairs of tentacles (except the Janellidae and I'crtigo, 

 which have only a single pair) ; these tentacles are invaginable, and the 

 eyes are borne on the summits of the posterior pair. The male and 

 female genital orifices open into a common vestibule except in the 

 Ditremata (Vaginulidae and Oncidiidae). A suprapedal gland is present 

 in nearly all the groups. With the exception of Uncidium, there is no 

 longer a veliger stage in the development ; the embryo is often furnished 

 with a contractile pedal vesicle (Fig. 117). 



The Sty lorn matophora may be divided into four tribes : the Holognatha, 

 Agnatha, Elasmognatha, and Ditremata. 



TRIBE 1. HOLOGNATHA. 



Jaw simple, without a superior appendage. 



FAMILY 1. SELENITIDAE, Fischer. Radula with elongated and 

 pointed teeth, like those of the Agnatha ; a jaw present. Genera 

 Selenites, Fischer ; shell external, depressed, widely umbilicated. Plutonia, 

 Stabile ; animal limaciform, with flattened internal shell and a posterior 

 pulmonary aperture. Triyonochlamys, Bottger ; no shell. FAMILY 2. 

 ZONITLDAE, Pilsbry. Shell external, smooth, heliciform or flattened ; 

 radula with pointed marginal teeth. Genera Zonites, Montfort ; 

 shell depressed, wholly external; British. Ariophanta, Desmoulins ; 



