600 Contributions to Invertebrate Palaeontology. 



MOLLUSCA. 

 GASTEROPODA. 



Genus MACROCHEILIJS Phillips. 



Macroclieilus regiilaris. 



Plate XV, fig. 13. 

 Loxonema regularis Cox, Geol. Rept. Ky., vol. iii, p. .'i66, pi. 8, fig. 2, 1857. 



Shell of moderate size, fusiform, with an elevated, rapidly ascending spire, 

 •which is composed of about nine volutions, and has an apical angle of from 

 twenty to twenty-five degrees, in diflerent individuals when not compressed. 

 Spire, when viewed in front, forming considerable more than half the length 

 of the shell, but when measured on the opposite side forms a little less than 

 one-half the entire length. Volutions slightly convex and in some individuals 

 presenting a slightly shouldered aspect caused by a very slight, almost imper- 

 ceptible angularity at about the upper third of the exposed part. Greatest 

 diameter of the body-whorl situated a little below the suture and decreasing 

 below. Suture close and not strongly marked. Aperture narrow, elongated, 

 the outer lip sharp and oppressed in the upper part. Columella twisted and 

 marked in the lower part by a single, but very strong twisted fold ; anterior 

 end of the lip rimate. Surface of the shell marked only by obscure lines of 

 growth. 



The species is one of the most elongated forms of the genus yet 

 recognized from the American Coal Measure strata, and will be 

 readily recognized by the great length of the spine, especially as 

 seen in a front view ; while the unusually strong columellar fold 

 will also distinguish it. In most of the specimens observed the 

 bod\^ volution appears to contract more abruptly above in its outer 

 half than before, giving a somewhat unsymmetrical feature to this 

 part of the shell. All the examples seen are compressed in the 

 direction of bedding, usually to the extent of one-third of their 

 original diameter or more, and some of them are entirely flattened. 

 This gives them in appearance a much greater apical angle than 

 the living shell really possessed, which may easily mislead one 

 in making a hasty comparison. The longest individual observed 

 measures two inches and five-eighths in length, and has a diameter 

 of the body-whorl of one inch. The shell is considerably flattened 

 except in the upper part of the spire, which shows the diameter of 

 the lower part to have been increased fully one-third. The species 

 was originally described by Prof. T. C. Cox, loc. cit., as a Loxo- 

 nema, and his figure would indicate a shell like Folyphemopsis, but 

 feeling uncertain of its accuracy in consequence of the great simi- 



