332 
APPENDIX. 
anfractus quatuor obtuse angulatos exbibente ; latere dextro excavato, anfractus duos cum 
dimidio cstendente; apertura ovato-triangularis, interdum utroque valde expansa.—PI. XI, 
figures 12, 13, 14, 15, 16, 17, and 18. 
Shell diseoidal, attaining a large size, delicately striated, of a watery-white color ; when laid 
upon the right side the shell has a remarkable conical or dome-shaped aspect, the extreme 
periphery being in a plane with the right side or base, from which the whorl grapually slopes 
upwards, terminating at the summit in a broad and deep concavity, exhibiting four well-marked, 
obtusely angulated whorls; the right side is decidedly concave, exhibiting two and a half or three 
well-rounded volutions. Aperture ovate-triangular, in 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 expands 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 diameter 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-eighths of an inch. 
Locality. —Found in the Colorado Desert; and also by Dr. Webb. 
I have associated specimens differing greatly in size and in developement of the aperture, hut 
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; hut 
besides the form of the volution and the consequent shape of the aperture, that shell is more 
coarsely striated, the whorls on the right side lie nearly in the same place, and on the left side 
hut two whorls appear. It differs from P. trivolvis , Say, in nearly the same particulars. In 
external surface it is more like P. glabratus, Say. 
AMNICOLA, PROTEA, Gould. 
[ Proceed. Bost. Soc. Nat. Hist., Y. 129. Mar. 1855.] 
T. parva, elongata, gracilis, variabilis ; anfractibus 7-8 convexis, profunde discretis, sim- 
plicibus, vel filis volventihus et costis longitudinalibus varie ornatis et clathratis: apertura 
ovata; labro continuo, simplici, anfractum penultimum vix attigente. PI. XI, figures, 6, 7, 
8, and 9. 
Shell small, turreted, 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 throughout, or more 
frequently sculptured with revolving threads or longitudinal 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 ipch 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 Melanim. It varies greatly also in its relative proportions 
of length and breadth. It is as slender as A. attenuata, Haldeman, and much larger. [This 
appears to he the same shell as that subsequently described by Mr. Conrad, under the name of 
Melania exigua .] 
