NATURAL SCIENCES OF PHILADELPHIA. 115 



One of the specimens of this species shows some indications of 

 having the immediate apical turn, as it were, very slightly un- 

 coiled, from which I am inclined to suspect that its embryonic 

 volution may have been reversed. This and the very small size 

 of the species seem to separate it from the typical Loxoneraas 

 and approximate it to Turhonilla. If its apex really was re- 

 versed, it should be placed in the latter genus, with the name 

 written Turhonilla attenuata var. semicostata. 



Locality and jJosition. Shale over the coal-bed at Danville, 

 Illinois. 



MTJECHISONIA OBSOLETE, Meek. 



Shell small, conical; spire moderately prominent, with lateral 

 slopes, straight, or sometimes very slight!}' concave a little above 

 the middle, rather attenuated near the apex ; volutions about ten, 

 compactly coiled, and regularly and gradually increasing in size 

 from the apex, compressed convex ; last one not enlarged, or more 

 produced below than in proportion to the general increase in the 

 size of the others, somewhat prominently rounded, but not even 

 subangular below the middle; aperture subrhombic, being a 

 little longer than wide, angular above, apparently angular or ef- 

 fuse on the inner side below, and rather abruptl}' rounded on the 

 outer side belov/ the middle, while the arcuate character of the 

 columella gives a rounded appearance to the middle of the inner 

 side ; suture deepl}^ impressed ; spiral band very obscure, being 

 flat, even with the surface, and onlj' defined by the faintest possi- 

 ble impressed line along its upper and lower margins. Surface 

 almost entirely smooth, but showing, when closely examined, very 

 obscure traces of marks of growth curving strongly backward as 

 the}' approach the spiral band, which passes around rather less 

 than, its own breadth above the suture on the volutions of the spire. 



Length of largest specimen, 0.95 inch; breadth, O-St inch. 



This species will be at once distinguished from the last, by its 

 shorter and more compactly coiled volutions, and almost entirely 

 smooth surface, on which no traces of revolving lines, or of the 

 distinct regular lines seen on that shell, occur. It also wants 

 the impressed line immediately below the suture of 3L loxone- 

 moides. It is very peculiar in having the revolving band almost 

 entirely obsolete. 



Locality and position, same as last. 

 1871.] 



