217 



Planorbis gracilentus. T. discoidea, compressa, albida, con- 

 einne striata ; latere dextro planulato ; latere sinistro modiee concavo; 

 utrinque anfr. 4 rotundatis, extemo ad peripheriam obtuse angulato : 

 apertura perobliqua, rotundato-ovalis. Axis |-; diarn. \ poll. The 

 Great Colorado Desert, low lands. Dr. T. H. Webb. 



No North American species, of equal size, can be compared with 

 this well-marked, wheel-shaped species. Very small specimens are 

 like very large ones of P. deflectus, Say. [The figure of P. Halde- 

 manni Dunker, (1841,) looks much like it.] 



Q^= Vol. v. 129, (March, 1855.) 



Amnicola protea. T. elongata, gracilis, variabilis ; anfr. 7-8 

 rotundatis, profunde discretis, simplicibus vel liris volventibus et costis 

 longitudinalibus varie ornatis et clathratis : apertura ovata ; labro 

 continuo, simplici, anfractum penultimum vix attigente. Long, (ex- 

 empli maximi) 0.3 ; lat. 0.1 poll. Colorado Desert (Gran Jornada). 

 Dr. T. H. Webb; W. P. Blake. 



Peculiar from its large size and slender form, though differing 

 greatly in relative proportions. It differs from all others, in being 

 variously sculptured with revolving ridges and longitudinal folds, like 

 most Melanias. [Mr. Conrad has described it under the name of 

 Melania exigua (read February, 12, 1853),]. 



Amnicola longinqua. T. parva, elongato-ovata, glabra ; apice 

 obtuso ; anfr. 5 rotundatis ; sutura profunda : apertura elliptica, postice 

 rotundata ; columella valde arcuata sub-perforata. Long. 1 ; lat.jL 

 poll. Found in the Colorado Desert (Cienaga Grande), by W. P. 

 Blake. 



Much like A. Cincinnatiensis, Hald. in form ; or like A. galbana or 

 miniature specimens of Palud. ponderosa, Say. It has a bleached or 

 chalky color, probably from exposure. The region is immersed a 

 portion of the time, and dry the remainder ; and was once, apparently, 

 an extensive marsh, or shallow lake. 



D^=» Vol. v. 228, (Oct. 1855.) 



Unio bracteatus. T. transversa, oblongo-ovata, solidula, sub- 

 ventricosa, tenuiter striata, flavo-viridis viridi saturation radiata, 

 antice rotundata, postice subacuta; umbonibus ad trientem anterio- 

 rem sitis, elevatis, utroque angulatis ; marginibus dorsalibus et ven- 

 tralibus lente arcuatis ; dentibus cardinalibus perobliquis, compressis, 

 duplicibus ; dentibus lateralibus arcuatis ; margarita argentea aureo 

 bracteata ; limbo iridescente. Long. 2^ ; lat. 1 ; alt. If poll. From 

 Llanos River, Upper Texas. Dr. T. H. Webb. 



In size, shape, and color, like U. Ogeecheensis, but the nacre and 

 position of the beaks are different. U. Hydianus is more inflated, 



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