Xo.2.] AVHITE ON CARBONIFEROUS AND CRETACEOUS FOSSILS. LU 7 



couveiiieut form of expressing- such recognition is thought to he the 

 aijplication of a separate specific name. 



This, together with the five following Carboniferous forms, was 

 obtained by Mr. G. K. Gilbert from "Wild Band Pockets, Northern 

 Arizona, 15 miles south of Pipe Spring." The strata from which these 

 fossils came are the uppermost of the Carboniferous series exposed at 

 that locality; and Mr, Gilbert thinks that, although they belong near the 

 top of the full Carboniferous series, there are in that, region some strata 

 which belong above them in that series. 



Genus Nucula Lamarck. 



Nucula penimbonata (sp. nov.)- 



Shell small, compact, ventricose ; posterior end obliquely truncated 

 from the beaks to the postero-basal border, its plane forming an acute 

 angle with that border; basal border broadly convex ; front abruptly 

 rounded; umbones large, much elevated; beaks situated about mid- 

 length of the shell, incurved, pointing a little downward and backward ; 

 umbonal ridges forming a right and left angular border to the broad 

 concave posterior or postero-dorsal space. Surface marked by fine 

 raised concentric lines. 



Length, 9 millimeters; height, from base to umbo, 6^ millimeters; 

 thickness, both valves together, Q^ millimeters. 



The collections obtained by Mr. Gilbert contain only a single speci- 

 men of this species ; but it is so nearly perfect, and its characteristics 

 are so well marked and so diiferent from those of smy known forms, that I 

 venture to give it a new specific name. In some of its characteristics this 

 shell resembles the young of the Miculana just described, judging from 

 the course of the concentric lines upon the umbones of that shell, but 

 it is not prolonged posteriorly like N'uGidana, even in its young state ; 

 besides which the shell in question is much more ventricose than the 

 young of that species could have been. It differs from other known 

 Carboniferous species of Nucula in the subcentral position of its beaks, 

 its large prominent umbones, and the broad concave space between its 

 umbonal ridges. 



Position and locality. — Carboniferous strata, associated with the pre- 

 ceding and four following species at Wild Band Pockets, Northern 

 Arizona, 15 miles south of Pipe Spring. 



Genus Allorisma King. 



Allorisma? gilberti (sp. nov.)- 



Shell rather small, elongate, broadly reflexed when adult, but less so 

 when young; posterior portion compressed and apparently slightly 

 gaping; valves broadly cou vex except posteriorly, where they are fiat- 

 tened or compressed, nowhere gibbous; antero-dorsal portion of the 

 shell obliquely truncated downward and forward, directly from the 

 Bull. V, 2 5 



