92 Mr. W. H. Benson on the Shell and Animal of Hybocystis. 



which must then be restricted to the other species presenting 

 oval peristomes as their title to distinction under that term, 

 whether sectional or generic. 



Hybocystis, nobis, nov. gen. 



Testa distorte ovata ; anfractus penultimus antice supra aperturam 

 planatus; apertura (species typicse) circularis, callum internum 

 superne sinuatum, a peristomate interiore sulco profuude excavato 

 divisum, exhibens. 



Operculum testaceum, crassum, extus concaviusculum, plurispiratum, 

 anfraetibus sensim accrescentibus, ultimo extus setate sensim 

 attenuate, junioris abrupte desinente, intus 1-i-spiratum, epider- 

 mide cornea nitida vestitum, medio foveato-umbonatum, anfractu 

 ultimo elevato priores partim celante. 



In H. gravida the animal is pale ; the foot short and oval, 

 slightly pointed posteriorly, the sole plane and entire; the 

 muzzle short, and emarginate in front and centre, the lateral 

 lobes short and rounded; tentacula ringed, grey, moderate, and 

 subulate ; eyes black, on a pale prominence or tubercle at the 

 outer base of the tentacula, and sessile on the head, not on the 

 side of the tentacula. The operculum is carried towards the 

 right side, and nearly at the extremity of the foot. A bright 

 reddish organ occupies the lingual region internally. 



The examination of living specimens of Otopoma clausum, 

 Sow., from Kattiwai*, enables me to contrast the animal of that 

 shell with Hybocystis. In O. clausum the foot is moderate in 

 length, and composed of two long, narrow, parallel soles sepa- 

 rated by a deep sulcus, and having also a deep sinus between 

 them at cither end. The muzzle is greatly elongated, emargi- 

 nate in front ; and the lateral lobes are capable of considerable 

 extension. The tentacula are moderate, hyaline, ringed, tumid, 

 and obtuse at the extremity. The eyes are prominent on the 

 outer side of the tentacula near their base, not sessile on the 

 head. 



On communicating to Mr. Theobald a remark on the peculiar 

 sole of this animal, he stated that he had noticed it, and that its 

 use was to enable the species to cling to the thin steins of the 

 branches of the shrub which it frequented near the shore of 

 Gopnath Point, on the Gulf of Cambay. The leaves which he 

 forwarded were kindly examined for me by Sir. W. J. Hooker, 

 and were pronounced to be those of Grewia betulifolia, DeCand., 

 an inhabitant also of Arabia, whence Sowerby's type specimens 

 of 0. clausum were procured. 



The head of a young Hybocystis was forwarded to Mr. Wood- 

 ward, for examination of the lingual teeth, on the 14th inst. 



