GO LAND AND FRESH-WATER SHELLS OF N. A. [pART IV. 



longer and more convex. It bears the same general relation 

 to undulatuvi that Troostii does to canalkulatum ; and these 

 shells may prove to be only tuberculate varieties of the others. 



Excuratum is a much longer, narrower species than either 

 of the above, with the whorls almost flat, and the upper ones 

 thickly striate. This feature is most apparent in the young 

 shell (Spillmanii, of Lea). 



MoniUfernm is not so narrow in its proportions as excxi- 

 o'atum, and is generally beautifully banded. It differs from 

 excuratum in the young shells being smooth instead of striate 

 on the spire. 



6. P. nobile, Lea. 



MeUmm nohilis. Lea, Philos. Proc, iv, p. 105, Aug. 18^15. Philos, Trans., x, p. 05. t. 



9, f. 48. Obs., iv, p. 05. BlXXEY, Check List, Ko. 179. 

 lo nohilis, Lea, Adams, Genera, 1, p. 299. 



Description. — Shell tuberculate, conical, rather thick, yellowish 

 horu-color; spire elevated; sutures irregularly undulate; whorls 

 flattened, in the middle tuberculate ; aperture rather large, elongated, 

 angular, and channelled at the base, within jellowish; columella 

 twisted. 



IlahitaL — Alabama. 



Diameter, -72; length, 1-7 inches. 



Observations. — This is among the finest of our American species. 

 It is remarkable for its large size and extended sinus, which allies it 



to the genus lo, in which it might, with no great 



Fiff. 114. 



irapropriet}', be placed. The specimen before me 



has eight whorls, and the broken apex would prob- 

 ably present about three more. The central ones 

 have a dark baud below, and ai'e of a rather bright 

 horn-color above. In this specimen there is a 

 rather coarse stria above the row of tubercles, and 

 two smaller ones below. The margin of the outer 

 lip is quite sinuous. It has some resemblance to 

 J/, excnrata, Conr., b«t may be distinguished by 

 having a larger fuse, and in the position of the 

 tubercles, which are not oblique, as described in 

 that shell. When other specimens shall be observed it may be found 

 lo difl'er in some of the characters described above. Aperture rather 

 more than one-third the lengtli of the shell. — Zica. 



