APPENDIX. 



CATALOGUE Continued. 



331 



I. FRESH-WATER SHELLS FROM THE COLORADO DESERT. 



PHYSA HUMEROSA, Gould. 

 [Proceed. Bost. Soc. Nat. Hist., V. 128. Feb. 1855.] 



T. solidula, subrhomboidea, polita ; spira acuta, anfractibus quinque tabulatis ; apertura 

 ^ ad | long ; idtudinis testse adequans, postice obtusa ; labro expanse, columella vix plicata. 

 PL XI, figures 1, 2, 3, 4, and 5. 



Shell rather large and solid, subrhomboidal, polished; all the specimens seen, (quite numerous, 

 and apparently not weathered,) porcelain white. Whorls five, each with a broad, square 

 shoulder, and forming an elevated, acute spire ; aperture usually about two-thirds the length 

 of the shell, sometimes but little over one-half; posterior angle obtusely rounded; outer lip 

 slightly flaring, when viewed in profile it is slightly advanced posteriorly so as to form a recess 

 at the junction ; pillar without any conspicuous fold, thickly covered with enamel, broadly 

 rounded and expanded at the base. Umbilical region nearly perforate. 



Length of an ordinary specimen, half an inch ; breadth, three-eighths of an inch ; length of 

 a variety, seven-tenths of an inch. 



Found in the Colorado Desert, by W. P. Blake ; also at Pecos River, by Dr. T. H. Webb. 



The broadly tabulated whorls, with the acute, elevated spire and foldless pillar, clearly dis- 

 tinguish this species. P. tab-data, Gould, from New Zealand, is similar, as well as some 

 varieties of P. ancittaria, Say, as figured by Haldeman, especially his figure 7, which he desig- 

 nates as a monstrosity ; but the spire is more elevated, and the deep suture always renders the 

 whorls distinct, and the absence of a columellar fold is a still further distinctive mark. It 

 would be difficult to distinguish the young by themselves from several other species, though they 

 begin to show the angularity of the whorls quite early. 



PLANORBIS AMMON, Gould. 

 [ Proceed. Bost. Soc. Nat. Hist., V. 129. Mar. 1855.] 



T. magna, discoidea, subconica, subtiliter striata ; latere sinistro late et profundS concavo, 



