59 
Corsuta Lavis. Corb. testd ovali, equilaterali, pallidd, tenui, le- 
vigatd, complanatd ; valve dextre margine ventrali acutd, pro- 
ductd ; umbonibus rectis, suberosis. Long. 6; lat. 25; alt. 4 lin: 
Hab. Hong-Kong, China. 
Cab. Belcher et Cuming. 
Both valves are flattened towards their ventral margins in a very 
characteristic manner. 
CorsuLa rasa. Corb. testd ovali, subequilaterali, elevatiusculd, 
tenui, levigatd, pallide fusco trifasciatd, postice ab umbonibus 
angulatd ; valve dextre margine ventrali acutd, productd ; um- 
bonibus rectis, fragmentis epidermide tenui indutd. Long. 5; 
lat. 12; alt. 22 lin. 
Hab. St. Miguel, east coast of Luzon, Philippine Islands. Ob- 
tained in the mud at low water. 
Cab. Cuming. 
It is very probable that the four species last described affect situ- 
ations where the water is brackish rather than salt ; and though they 
retain the hinge of Corbula, in general character they materially 
differ from the more typical forms of the genus. 
Poramomya, J. Sowerby. 
PoramMomya nimBosa. Pot. testd ovato-trigond, levigatd, antice 
rotundatd, postice productd, angulatd ; valvis inequalibus, margine 
ventrali acutd; umbonibus subequalibus ; epidermide tenui, tene- 
brosd, indutd, lineis capillaribus radiantibus ; intis albidd. Long. 
17; lat. 8; alt. 11 lin. 
Sowerby’s Conch. Manual, f. 498, 499. 
Hab. The tributary streams of the Rio de la Plata, in the mud. 
Cab. Cuming. 
Poramomya ocrEATA. Pot. testd valde inequilaterali, antice abbre- 
viatd, rotundatd, postice productd, subnasutd, ab umbone ad mar- 
ginem posticam angulatd ; valvd dextrd rotundatd, margine ven- 
trali antice productd, acutd ; epidermide fusca indutd ; intts albidd 
vel cerulescente. Long. 13; lat. 6; alt. 8 lin. 
Hab. Brazil. From freshwater streams. 
Cab. Cuming et Metcalfe. 
The younger specimens are much less inequilateral than the old. 
The following descriptions of new species of Shells belonging to 
the genus Cyclostoma, by Mr. G. B. Sowerby, were then read. 
CycLostoma PusiLLum, nob., Thes. Conch. part 3. pl. 23. f. 55*. 
Cycl. testd orbiculari, subdiscoided ; apice spire subprominulo ; 
anfractibus quatuor, rotundatis, lineis incrementi solitm striatis ; 
’ suturd profundd ; aperturd circulari, peritremate tenuiusculo, sub- 
reflero, postice prope anfractum ultimum subemarginato ; umbilico 
patulo ; operculo multispiral, extiis concavo, margine canaliculato, 
intis nitido. 
