166 Bulletin American Museum of Natural History (Vol. LITI 
Hydrocenidze 
Shell small, imperforate, globose-conic, with thickened columella. Operculum 
corneous, with concentric strie, with a projecting process articulating with the 
columella. 
Animal amphibious, with short, broad tentacles; the eyes placed at their external 
bases. Respiration by means of a lung. Radula with the teeth of the central field 
very small or absent; outer laterals not capitulate; the marginals extremely numerous 
and closely imbricate, in strongly oblique rows. 
_ These minute snails are mainly found in the littoral zone. Only one 
species is known thus far from the Ethiopian Region. 
Hvyorocena Pfeiffer 
Hydrocena “‘Parreyss”’ Preirrer, July, 1847, Zeitschr. f. Malakoz., IV, p. 112. 
Type by original designation: Cyclostoma cattaroensis Pfeiffer. The name was 
published as a nomen nudum by Herrmannsen (May, 1847, ‘Ind. Gen. Malac.,’ I, 
p. 546). 
Ethiopion species: , 
Hydrocena n, 1856 noticola Brmnso, Ann. Mag. Nat. Hist., (2) XVIII, p. 4389= 
Assiminea tyttha MELVILL AND PonsonBy, 1897, op. cit., (6) XIX, p. 639, Pl. xv11, 
fig. 11. Near Cape Town (ravine overlooking Camp’s Bay), Cape Colony (type 
locality). 
PECTINIBRANCHIATA TAENIOGLOSSA 
Ampullariide 
Medium-sized, large or very large, dextral or (apparently) sinistral snails, the 
shell moderately thick to very thin; ovate, globose-conic or subspherical, rarely much 
depressed or planorboid; usually perforate or broadly umbilicate, or rarely the umbili- 
cusis closed. The surface is usually smoothish, sculpture if present being microscopic; 
sometimes it is malleate, or with prominent growth wrinkles, more rarely with spiral 
grooves or carine. Operculum completely closing the aperture, with nucleus sub- 
median near the columellar margin, and concentric increment. It is either thin, 
flexible and wholly corneous, capable of retraction some distance within the mouth; 
or rigid, thickened by an internal calcareous layer,!in which case it lodges at the peri- 
stome. The scar attachment is within the columellar half of its width. 
The animal is dextral. The head has long, tapering tentacles and prominently 
stalked eyes at their exterior bases. Muzzle stout and conspicuous, terminating in 
two long, tapering labial processes. Anterior edge of the foot doubled. Enpipodial 
lobes, adjacent to the eye-stalks, form left Gnhalent) and right (exhalent) conduits. 
The penis arises from the right side of thé thick mantle-edge and is carried folded back 
in the cavity Mantle cavity containing a monopectinate gill adnate throughout; 
it is divided by a partition attached to the mantle, perforated subcentrally or on the 
left side, and segregating an upper-left chamber which functions as a lung. The 
mouth is provided with a pair of large jaw plates and a relatively large radula. The 
1The operculum of Pila has been erroneously described as “‘ externally caleareous’’ (1904, Journ 
] ‘ . Of 
Conchology, XI, p. 52). The external layer is always corneous, the calear2ous layer being within. 
