NATURAL SCIENCES OP PHILADELPHIA. -^5 



Locality and i^osition. Columbus, Ohio. Coriiiferous <rroup 

 of Devonian series. '^ 



PLATYCERAS ATTENUATUM, Meek. 

 Shell attaining a moderate size, very slender and elongated. 

 Body part more or less arched above, a little compressed behind,' 

 subangular on the right side, rounded over the dorsal or anterior 

 slope, and gradually tapering backward to the small free apex, 

 which is composed of one to one and a half contiguous volutions,' 

 and twisted to the right of the longitudinal axis of the free bod3^ 

 Aperture irregularly oval or suborbicular, and comparatively 

 small or little expanded ; lip most produced on the right anterior 

 side, and sometimes a little retreating behind, with one or two 

 other faint, smaller undulations of its margin around the front. 

 Surface of cast without longitudinal plications, folds, or undula- 

 tions, but showing over the dorsal and anterior slope numerous 

 small tubercles that evidently mark the positions of spines on the 

 exterior. Surface markings of the shell itself unknown. 



Length of the largest specimen, measuring direct from most 

 prominent part at the curve of the spire to that of the anterior 

 margin of the aperture, 2.10 inches; do. measuring from the apex 

 over the dorsal curve to the same, about 3.70; greatest breadth 

 of aperture, 1.35 inches. 



This shell seems to differ from all of the described spiniferous 

 species with which I am acquainted, in being more slender, more 

 elongated, and in having the small apex twisted nearly at right 

 angles to the axis of the body part. These characters appeaAo 

 distinguish it readily from the typical P. dumosum, Conrad ; while 

 from the variety of that species that has been described under the 

 name rarisjnnum^ it differs in never having its body even "mode- 

 rately ventricose," nor in any case in contact with the apical 

 coils, as well as in having more numerous spines, if we can judge 

 from the number of tubercles, of which about fifty may be counted 

 on the specimen from which the foregoing description was made 

 out. 



In general form it resembles the more slender individuals of the 

 non-spiniferous species P. rejiexum, from the Oriskany sandstone, 



' I describe such forms, for convenience, as if placed with the aperture 

 downward and the apex directed backward toward the observer. 

 1871.] 



