42 



pernotabili, acuta. Long. § , lat. £ poll. Hai. Lake Vancouver, 

 Oregon. 



Allied to L. pallida, Adams, but is more delicate, more acute- 

 ly pointed, the aperture much larger, the lip expanded, and the 

 surface peculiarly decussated. The whorls are much more ob- 

 lique and less rounded than in L. desidiosa. 



Planorbis opercularis. Testa parva, valde depressa, casta- 

 nea, supra planulata ; apice depressa : subtus convexa, late 

 umbilicnia, ad peripheriam marginata et obtuse carinata ; spira 

 anfr. 4, sutura bene impressa sejunctis ; apertura transversa, sub- 

 rhomboidea. Long. ^, lat. y 1 ^ poll. Hab. Rio Sacramento, 

 Upper California. 



Resembles P. exacutus, Say, but is larger, less compressed and 

 less delicate ; and the periphery instead of being acutely edged, 

 has a blunted keel like P. carinatus. 



Planorbis vermictjlaris. Testa parva, fornicata : spira plan- 

 ulata, apice depresso, anfr. 4, cylindraceis, ultimo prope aper- 

 turam deflexo : subtus concava ; apertura perobliqua, elliptica. 

 Lat. i, alt. y 1 ^ poll. Hab. Interior of Oregon. 



About the size and form of P. dejlectus, Say, but is less de- 

 pressed, the whorls more cylindrical, and not compressed at the 

 periphery. 



Phvsa tabulata. Testa ovata, sub-solida, impolita, fuligino- 

 sa ; spira anfr. 4-5 ventricosis, superne angulato-carinatis, late 

 tabulatis : apertura elliptica, dimidiam testae longitudinis super- 

 ans ; columella albida, vix plicata. ; fauce fusco-castaneo. Long, 

 •/o, lat. iV ; poll. Hab. New Zealand. 



Not to be mistaken for any other species. It is very much 

 more angular than P. ancillaria, and the keel upon the angle, 

 when closely examined, is found to be minutely crenulated. 

 P. variabilis, Gray, has the lower instead of the upper part of 

 the whorl angular and keeled. 



Phvsa gibbosa. Testa obovata, tenuis, glabrata, luteo-cornea : 

 spira acuminata, anfr. 5 rotundatis, ultimo postice valde gibboso, 

 antice attenuato ; apertura angusla, subovalis, trientes duae lon- 

 gitudinis adequans ; columella sinuata, callo induta. Long, f, 

 lat. f poll. Hab. New South Wales. 



