No. 2.] WHITE ON CARBONIFEROUS AND CRETACEOUS FOSSILS. 219 



all localities. B. carbonarius is also constant in its smaller size, tlirougli- 

 oiit its wide distribution in the great Mississippi Yalley, and its great 

 vertical range in the Coal-measures there. The other characteristics 

 which distinguish the two species are also constant in their range and 

 distribution respectively. The more conspicuous one of these character- 

 istics, as regards B. suhimiriUosns, consists in the studding of the surface 

 of the outer part of the last volution, which is plain in B. carhonariiis, 

 with slightly raised pai^illce, which are arranged in rows, corresponding 

 to and continuous with the revolving strife. 



B. suhpa2nUosiis is characteristic of the ui^per strata of the Carbon- 

 iferous series in j^orthwestern Colorado and the adjacent region; and its 

 l)resence among the cojlections from Northern Arizona seems to indicate 

 a similar horizon for the strata from which the latter were obtained. 



Genus Muechisonia D'Archiac. 



Murchisonia terebra (sp. nor.). 



Shell slender; apical angle 16^ or 17°; full number of volutions 

 in adult examples not less than seventeen or eighteen; volutions 

 strongly angulated, with only one angle, which is slightly carinated and 

 finely nodulated, and situated much nearer to the proximal than the 

 distal border of the volution ; outer side of the volution, between the 

 distal border and the carinated angle, straight, and slightly concave 

 between that angle and the proximal border; suture shghtly impressed, 

 moderately distinct. The whole outer surface of the volutions on both 

 sides of the angle marked by fine revolving raised lines of nearly 

 uniform size. 



This species differs conspicuously from any published form of the 

 genus in possessing the single prominent angle situated near the i)roxi- 

 mal border of the volution, and the broad flattened outer side of the 

 volution between the angle and its distal border. It is perhaps more 

 nearly related to M. marcouiana Geinitz, from the Upper Coal-measures 

 of Eastern Nebraska, than any other known form; but it differs from 

 that species in the character and position of the prominent revolving 

 angle, in having a much greater apical angle, and in wanting the 

 numerous uniform revohing raised lines which mark the whole outer 

 surface of 31. terehra. 



The full length of the largest example in the collection would be, if 

 perfect, not less than 45 millimeters. 



Position and locality — Associated with the preceding in Carboniferous 

 strata at Wild Band Pockets. jSTorthern Arizona. 



Genus Pleueotomaria Defrance. 



Pleurotomaria grayvillensis Norwood & Pratten. 



A couple of imperfect examples of a small Pleurotomaria, brought by 

 Mr. Gilbert from Wild Band Pockets, Northern Arizona, with the four 

 preceding species, correspond too nearly with the description and figures 



