24 H. Doc. 129. 



middle-sized specimens projecting about equally to either side, in 

 small specimens projecting to the right side only, and in the largest, 

 spreading amply to both sides, and especially the right, where it ex- 

 pands and forms a remarkable ear-shaped aperture. 



Diameter of the disk, in the middle-sized specimens, five-eighths of 

 an inch, and in the largest, one inch ; axial dimater of the first, one- 

 fourth of an inch, of the latter, half an inch; and in one specimen 

 the breadth of the aperture, from side to side, is five-eights of an inch. 



Locality. Found in the Colorado desert ; and also by Dr. Webb. 



I have associated specimens differing greatly in size and in develop- 

 ment of the aperture, but all agreeing in the peculiar slope of the 

 outer volution, giving a conical outline when lying on the side. The 

 fully developed specimens have the general aspect of P. corpulentus, 

 Say ; but besides the form of the volution and the consequent shape 

 of the aperture, that shell is more coarsely striated, and the whorls 

 on the right side lie nearly in the same place, and on the left side but 

 two whorls appear. It differs from P. trivolois, Say., in nearly the 

 same particulars. In external surface it is more like P. glabratus, Say. 



AMNICOLA PROTEA, Gould. 



T. parva, elongta, gracilis variabilus ; anfractibus 7-8 convexis, 

 profunde", discretis, simplicibus, vel filis volentibus et costis longitu- 

 dinalibus varie ornatis et clathratis ; apertura ovata ; labro continue , 

 simplici, anfracturn penultimum vix attigente. PI. , fig. . 



Shell small, turretted, slender, greatly elongated, chalky white, 

 (so far as seen_,) variously proportioned, composed of seven or eight 

 whorls, which are either convexly rounded or broadly shouldered, 

 and separated by a deep suture the surface either smooth through- 

 out or more frequently sculptured with revolving threads or longitu- 

 dinal ribs or decussated by both in various proportions, the upper 

 whorls being in nearly every instance decussated, aperture ovate, lip 

 simple, continuous, generally detached from, or scarcely appressed to 

 the penultimate whorl, in many instances leaving an umbilical chink. 



Largest specimens three-tenths of an inch long and half an inch 

 broad. 



Found in the Colorado desert; also by Dr. T. H. Webb. 



This species is peculiar on account of its elongated, slender form, 

 and differs from the other species of the genus yet described in being 

 variously sculptured with revolving ridges and longitudinal folds 

 like many of the Melanise. It varies greatly also in its relative pro- 

 portions of length and breadth. It is as slender as A. attenuata., Hal- 

 deman, and much larger. 



AMNICOLA LONG1NQUA, Gould. 



T. parva, elongato-ovata Irevis, apice obtuso, spirx anfractibus 

 quinque rotundatis, sutura profunda discretis: apertura elliptica. 

 postice, rotundata; columella profunde arcuata. PI. , fig. . 



Shell small, elongate ovate, horn-colored, (or blanched chalky white^) 

 surface quite smaoth ; apex obtuse, whorls five, well rounded and sep- 



