FOSSILS OF THE COAL MEASURES. 599 



MriH HISOX1A INnRNATA, M. and TV. 



PL 28, Fig. 6. 

 Mnretritonia itwrnata, MEEK and WOBTHEX, 1866. Proceed. Acad. Xat. Sci., Phila.. p. 274. 



SHELL very small, conic sub-ovate; axis imperforate; 

 spire rather short (for a Jfurchifionia); volutions six, con- 

 vex, increasing rather gradually in size, last one form- 

 ing more than half the entire shell, most prominent around 

 the middle, but not even obtusely angular, a little pro- 

 dueed below: suture impressed; aperture slightly oblique, 

 sub-ovate iu outline, being angular above and rounded and 

 apparently faintly effuse below; spiral band not distinguish- 

 able from the general surface of the whorls, excepting as 

 indicated by the curve of the minute lines of growth seen 

 by the aid of a magnifier, apparently of moderate breadth, 

 and placed about half way between the middle and the 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 stria*, most dis- 

 tinct below 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 the undefined spiral baud. 



Length, 0.22 inch; breadth, 0.13 inch; apical angle, about 

 3-s degs. 



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

 determined by the shell alone, be referred, with almost equal propriety. 

 t<> either Murchiwnia or PleHrofrnnaria, though agreeing rather more 

 nearly with the former. It will be readily distinguished from all the 

 little species of either of these genera known to us, that agree with it, 

 in being without eostate or carinated whorls, by its nearly smooth sur- 

 face, by its nearly obsolete spiral band. Excepting in its much smaller 

 si/\ and less produced body whorl, it has somewhat the look of .!/>//- 

 cltixoiiin UK l<i/t<i!<lix. de Koninck (An. Foss.. pi. m, fig. 14, , ft,) but the 

 more produced lower part of the body whorl of that shell gives its aper- 



