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362 bulletin: museum of comparative zoology. 



representation of the genus in the Rocky Mountain Region, and 

 suggests the desirabiUty of obtaining further information upon the 

 occurrence of the genus in that region. 



The genus Schizoblastus has had a similar history. In 1874 White 

 described one species, Schizoblastus lotoblastus, from the Subcarboni- 

 ferous of Arizona, and in 1879 noted the same species from the Car- 

 boniferous of the Teton range. Dr. W. P. Haynes brought back from 

 the Carboniferous at Squaw Creek, Montana, three specimens of the 

 genus, which, owing to their imperfect preservation, he could not 

 distinguish from Schizoblastus lotoblastus. From the same locality 

 the writer collected several silicified specimens which, etched, were 

 plainly not conspecific with Schizoblastiis lotoblastus. 



A blastoid like Pentremites subconoidcus has been found at Frank, 

 Alberta, in the Carboniferous limestone, and indicates the occurrence 

 of blastoids in that part of the Rockies. 



Dr. K. F. Mather, in 1915, published The Fauna of the Morrow 

 Formation of /Arkansas (Bull. Sci. lab. Denison univ., 1915, 28, p. 59.) 

 in which he described two species of Pentremites from the Penn- 

 sylvanian. The possibility that the limestone at Old Baldy, or at 

 least the upper part of it, is of Pennsylvanian age has frequently been 

 considered. The Quadrant sandstone is certainly calcareous at its 

 base, and also fossiliferous. The only fossils directly associated with 

 the Pentremites found by the writer at Old Baldy are Hustedia mor- 

 vioni and Spirifcrina kentuckiensis, both of which indicate an Upper 

 Carboniferous horizon. We must therefore cease to think of the genus 

 Pentremites as becoming extinct with the close of the Mississippian, 

 and recognize it as extending, at least in the Rocky Mountains and 

 in Arkansas, over into Pennsylvanian time. 



I would suggest the advisability of comparing species of blastoids 

 not solely by means of written descriptions, but with the help of 

 actual measurements. Such measurements are at the same time both 

 a check upon the description, and in some ways a shorthand expression 

 of it. Frequently, disconnected measurements have been given in 

 descriptions of species but until Mather's paper no recognized set of 

 measurements had been used. It will be seen, however, that mere 

 listing of the actual measurements of blastoids will lead to endless 

 confusion unless we have a datum point to start from. I suggest, in 

 this connection, that actual measurements of Pentremites be adjusted 

 to a standard height for each specimen of twenty millimeters. Ob- 

 viously the measurements of adult forms only should be adjusted in 

 this manner, and each investigator must use his own discretion in 

 rejecting specimens too young to be treated. Individual variations 



