58 Zoological Society. 



PROCEEDINGS OF LEARNED SOCIETIES. 



ZOOLOGICAL, SOCIETY. 



July 9, 1851.— John Gould, Esq., F.R.S., in the Chair. 

 Description of a new genus of the Family Melaniana, 



AND OF MANY NEW SPECIES OF THE GeNUS MeLANIA, 



chiefly collected by Hugh Cuming, Esq.. By Isaac 

 Lea and Henry C. Lea, Philadelphia*. 



Genus Pachychilus*|\ 



Testa conica. Apertura ovata, basi integro. Labrum crassum. 

 Columella superne incrassata. Operculum suborbiculare, corneum. 



The genus Melania has been found to embrace such avast number 

 of species in various parts of the globe, that it has become very de- 

 sirable to separate any definite group with sufficient persistent cha- 

 racteristics. The thickened lip sufficiently distinguishes the proposed 

 genus from Melanopsis and Melania X- It differs from Melanopsis 

 also in its having no sinus, while it resembles it in the possession of 

 a thickened columella above. From Melania it differs also in having 

 this callous columella. The species on which it is proposed to found 

 this genus has a mouth looking like a thick-lipped Bulimus. The 

 operculum differs somewhat from that of any Melanian I have seen. 

 Its polar point is subcentral, from which two or three spiral revolu- 

 tions are made ; then a thinner margin surrounds these spirals. 



The animal has not been observed, and may and probably will 

 prove very different from Melania. Its proper position, however, in 

 the system will most likely be found to be between Melanopsis and 

 Melania, and there I would at present place it. 



A second and very distinct species may be added to this genus — 

 the Melania laevissima, Sowerby, described in Deshayes' edition of 

 Lamarck. It inhabits Colombia, and is a shorter, wider, and much 

 thicker shell, with a large white mouth. 



Pachychilus Cumingii. P. testd Icevi, elevato-conicd, sub- 

 crassd, nitidd,fusco-nebulosd; spird elevatd, acuminatd ; anfrac- 

 tibus undecim, convexiusculis ; suturis linearibus ; aperturd par- 

 viusculd, subrotundd, ad basim rotundd, intus fused ; labro valde 

 expanso ; columelld superne incrassatd. 

 Hab. Large rivers, Copan, Central America. 

 Length 1*4, diam. *5 of an inch. 



Remarks. — This is a very remarkable shell among the Melaniens. 

 It is of fine symmetry, the whorls being very regular to the apex. 

 The brownish cloudiness gives the whole surface a dark hue, while 

 the smoothness of the whorls gives it almost a polished appearance. 

 It differs very much in form from Melania Icevissima, Sow., which 

 naturally belongs to the same genus, and which is adopted above ; 



* All the species described are in the Cabinets of Hugh Cuming and Isaac Lea. 



t Hax^s, thick, and x e «'^os, tip. 



X Lamarck describes the family Melaniens as having a sharp outer lip, " le 

 droit toujours tranchant ; " but this genus naturally belongs to Melania, Mela- 

 nopsis, and Pirena. 



