GASTROPODA. "''' 



Lopbocptr* ml.| 



edge is merely wavy instead of toothed, while on the last or free whorl of old 

 specimens the prominences are, if not wanting entirely, at least much more irregu- 

 larly developed. In nil the Ixxly whorl has four nearly equidistant sharp carimc, 

 one on the upper slope a third or a little more of its width distant from the suture, 

 ;i third Iteneath tin- peripheral one already described, and a fourth marking the 

 limits of the rather large umbilicus. The latter has a distinctly convex slope, while 

 the space between the third and fourth keels is gently convex in the middle, those 

 between the peripheral one and the third and first decidedly concave, and that 

 between the summit of the first keel and the suture line more gently hollowed out. 

 \~ l"n_' as the whorls are in contact the upper edge is sharp so that the suture is 

 not excavated, but soon after the last turn becomes free this edge is lost, the whole 

 upper -urface. that i-, above the first carina. becoming almost uniformly rounded. 

 Aperture, excepting the angulation at the peripheral carina, subcircular; in a side 

 view the outer lip is deeply notched at the principal carina and somewhat angularly 

 produced at the extremities of the first and third keels. Surface marked with 

 regular strong sharp equidistant lines of growth on the upper whorls, the stria; 

 becoming more irregular and assuming an aged appearance on the free last turn. 

 Their number in a given space varies, but the average at the first or upper carina is 

 about three in 2 mm. The direction of the striae, beginning at the suture, is first 

 gently backward and then with a slight forward curve to the summit of the first 

 carina. I rom here they sweep regularly and very decidedly backward to the 

 peripheral keel, and beneath this forward again in a corresponding degree to the 

 third carina on which they make a rectangular turn and proceed with less curvature 

 than above to the fourth or umbilical keel. In the umbilicus, finally, the last 

 backward direction continues until overcome by the curve when a transverse course 

 is maintained until the circuit is completed on the upper side of the whorl. 



In casts of the interior of young individuals all save the first three whorls, 

 which are but rarely preserved, may preserve in a decided degree the angularity 

 which mark> the exterior, hut in fully grown examples only the last whorl retains 

 the angles and even here the peripheral carina only is distinct. (This is one of the 

 point* relied upon in di>tinir u i^i,i n g internal casts of this and the next species.) 

 We have very little doubt of the -perihV identity of this common shell of t,he 

 es River ^roup in Minnesota, Wisconsin and Illinois, with the Mun-hi- 

 serrulata described by Sailer from the Hlack River group of Canada.* We grant 

 that Salter neither mentions nor figures his species as having the la-t volution 

 uncoiled. l>ut this is readily explained if we as-unie. and his illu-tration justifies us 

 in doing so, that he had only young or imperfect examples. We have numerous 



With tbrtodtnc*olaUUlhl irrm Include* lh* BlrdMjr* or StOfm Rlr gr 



