186 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 with a posterior internal septum ; 
from New Zealand.  Gundlachia, Pfeiffer. Famity 11. Paystpas, 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. Apleza, 
Fleming ; shell with a pointed 
spire; edges of the mantle not 
divided and very slightly re- 
flected over the shell ; British. 
Fic. 176. 
Bre. Ancylus fluviatilis, dorsal 
Bulinus tabulatus, ventral aspect. view. To the left, the head 
br, pallial extrapulmonary gill; co, with the two cephalic ten- 
heart ; 0, mouth; p, foot; pa, mantle ; tacles. (From Lankester, after 
pns, pneumostome ; te, tentacle. Reeve.) 
Sup-ORDER 2. STYLOMMATOPHORA. 
Pulmonata with two pairs of tentacles (except the Janellidae and Vertigo, 
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 Uncidiwm, there is no 
longer a veliger stage in the development ; the embryo is often furnished 
with a contractile pedal vesicle (Fig. 117). 
The Stylommatophora may be divided into four tribes : the Holognatha, 
Agnatha, Elasmognatha, and Ditremata. 
TRIBE 1. HoLOGNATHA. 
Jaw simple, without a superior appendage. 
Famity 1. SeLeniripar, 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. Trigonochlainys, Bottger; no shell. Famimy 2. 
ZONITIDAR, Pilsbry. Shell external, smooth, heliciform or flattened ; 
radula with pointed marginal teeth. Genera— Zonites, Montfort ; 
shell depressed, wholly external; British. Artophanta, Desmoulins ; 
