t 



274 PROCEEDINGS OF THE ACADEMY OF 



MURCHISONIA INORNATA, M. & W. 



Shell very small, conic subovate ; axis imperforate'; spire short (for a Mur- 

 chisonia). Volutions six, convex, increasing rather gradually in size, last one 

 forming more than half the entire shell, most prominent around the middle, 

 but not even obtusely angular, a little produced below ; suture impressed. 

 Aperture slightly oblique, subovate in outline, being angular above, and 

 rounded and apparently faintly effuse below. Spiral band not distinguishable 

 from the general surface of the whorls, excepting from the curve of the minute 

 lines of growth, as seen by the aid of a magnifier ; apparently of moderate 

 breadth, and placed about half-way between the middle aud upper side of the 

 body whorl, passing around near the middle of those of the spire. Surface 

 appearing nearly smooth to the eye, but when examined with a magnifier, 

 seen to be ornamented with small obscure revolving striae, most distinct be- 

 low the middle of the body whorl ; crossing these, traces of very minute lines 

 of growth may be seen, by the aid of a good lens in a favorable light, curving 

 strongly backwards as they approach an undefined spiral band. 



Length, 0-22 inch ; breadth, 0-13 inch ; apical angle about 38. 



This is one of those intermediate forms, that might, so far as can be deter- 

 mined from the shell, be referred with almost equal propriety to either Mur- 

 chisonia or I'ieurotomarin. Although we have placed it in the former genus, 

 we are not sure but we should call it I'leurotomaria inornata. It will be readily 

 distinguished from all the little species of either of these genera known to 

 us, that have neither costate nor carinated whorls, by its nearly smooth 

 surface and obsolete spiral band. Excepting in its much smaller size, and less 

 produced body whorl, it has somewhat the look of Murchisonia melanoides, de 

 Koninck, (An. Foss. pi. iii. sup. fig. 14, a, b,) but the more produced lower 

 part of the body whorl of that shell gives its aperture a different form, while 

 it has a well defined spiral band occupying a lower position on the whorls, 

 and no traces of revolving lines. 



Locality and position. Hodge's Creek, Macoupen County, Illinois. Lower 

 Coal Measures. 



CEPHALOPODA. 



Nadtilus [Trematodiscus] sulcatus, Sowerby ? 



Amongst other specimens from the Chester group of St. Genevieve County, 

 Missouri, we have several examples of a small Nautilus, agreeing so nearly 

 with Sowerby's N. sulcatus that we are strongly inclined to believe it identi- 

 cal with that species. It attains about the same size, has a similar umbilicus, 

 the same number of whorls, with the same number of furrows and intermedi- 

 ate ridges on each side, and like that species has a small, nearly central si- 

 phon ; while it also agrees in the size and flexures of its lines of growth, as 

 well as in the variations it presents. The only differences we can see are 

 that our shell seems to have the whorls generally more compressed, and its 

 furrows and ridges sometimes more obsolescent on the outer volution of the 

 larger specimens. Still it generally agrees quite as nearly with the typical 

 forms of that species, as those usually referred to it by the most reliable 

 European authorities, and even more nearly than many of these do with each 

 other. (Prof, de Koninck's description of N. sulcatus agrees exactly with our 

 shell.) Its lines of growth make so strong a backward curve in crossing the 

 slightly concave, rather narrow periphery, that we were at first inclined to 

 think it a large Porccllia, but a closer examination soon satisfied us that it is 

 septate, and provided with a small, nearly central siphon. In short, it is a 

 typical example of the group for which wepropoSed the subgeneric name Tre- 

 matodiscus. 



We are not aware of this species having been previously identified in Ame- 

 rica. 



[July, 



