136 



Physa Cooperi, Teyon. 



Between the Auimas and La Plata, 5 specimens. 



Also recorded from aspringin Crane Lake Yalley, l!«I^ortheast California 

 (Gahl}). 



Eemarks. — I do not feel quite sure of this determination, because of 

 the immaturity of the specimens, and the fact that I do not have access 

 to types; nor do I altogether trust in the validity of the species. 



Buliniis hypnorum, Linn. 



Camp 9-10 : Grand Eiver Valley 50 specimens. 



Recorded also from Hell-Gate Eiver, Montana [Cooper); Utah; Ma- 

 lade River, Idaho {Remjyhill); Washington Territory; Yellowstone Eiver 

 {Smithsonian Catalogue)', British possessions (Lor<i) northward. 



PLANOEBINJE. 



Helisoma plexata, SP. NOV. 



Shell a little larger than P. Trivolvis, Say, of irregular inoportions, fra- 

 gile ; whorls 4-5, the inner 3-4 of the spire angulated and coiled in a plane, 

 which is consider ahly inclined to the plaiie of the outer revolution in such a 

 way that the carina of the third tchorl rises into a sharp shoulder on the right 

 side*, and on the left side sinhs underneath the overfloiving last ichorl, which 

 takes on a sudden increase in old age. A similar, hut less, change in the plane 

 often occurs again in the fourth whorl, giving a very ttvisted appearance to the 

 shell. Surface marh-ed by irregularly-crouided, tvavy, raised lines of groicth. 

 Umbilicus broad, exhibiting the tcell-rounded tchorls to the apex. Aperture 

 somewhat oblique, pretty regularly pyriform in outline, the vertical slightly 

 exceeding the horizontal diameter, and embracing a considerable portion of 

 the body ivhorl, icell to one side of the median line. Peristome gently reflected, 

 slightly thicliened icithin, and fully lined icith an opaque ivhite deposit, ivhich 

 also forms a thick and well-deflned callus coyinecting the ends. Color yellow- 

 ish horn to reddish-broivn (becoming almost black behind the aperture), most 

 specimens abundantly banded and streaked tvith revolving lines of ochraceous 

 red, ayidfine black threads. 



Saint Mary's Lake, Antelope Park 25 specimens. 



Eemauks. — This species existed in countless numbers in the above- 

 mentioned lake, which is a small sheet of water held among precipitous 

 cliffs, which afford it no visible outlet. Jt seems to be merely a " sink " 

 for the melted snow of the surrounding heights. All of the hundreds 

 of individuals seen, possessed, in a more or less marked degree, the 

 twisted appearance, resulting from the change of plane in the old age 

 of the shell, which is their most striking character. How the species 

 came, almost entirely alone, to inhabit this secluded lake is a problem, 

 complicated by the fact that there is not probably another large Plan- 

 orbis within fifty miles. That the wild Ibwl, abundant on the lake, 

 brought the eggs clinging to their feet, may be a plausible explanation ; 

 but where did they bring them from, and w^hen? The bottom of the 

 lake is, for the most part, rough, conglomerate rock, and it is in many 

 places filled with heavy water-plants, which may account for the pecu- 

 liarities of the shell. 



'^ As you hold the shell-spire upward, and look into the aperture. 



