CAMBRO-SILURIAN MICRO-PAL. EONTOLOQY. 6i> 



the three specimens seen, vary in diameter from two and a half to 

 eight mm. Surface even (i.e. without monticules), but in the largest 

 example exhibiting clusters of cells of larger size than the average. 

 Zooecia polygonal, thin-walled, with about eight of those of the 

 ordinary size in two mm. Acanthopores of moderate size, being 

 smaller than those of P.asperula, XJlrich, and P. petechialis, Nicholson, 

 and a little larger than those of P. gregaria, Ulrich. Most of the angles 

 of junction between the zooecia are occupied by them. Mesopores 

 absent. 



The result of my preliminary examination of these specimens was to 

 refer them to P. asperula, but a careful comparison with the types of 

 that form proves that they really belong to a distinct species. Indeed, 

 P. gregaria seems to be still more nearly related to P. scabiosa, differ- 

 ing thei'efrom mainly in its flat oj* concave upper surface and slightly 

 elevated marginal band. P. asperula has smaller zooecia (eleven in 

 two millimetres), a monticulated surface, and stronger acanthopores. 



Stony Mountain, Manitoba, Dr. E. W. Ells, 18*75, and Mr. T. C. 

 Weston, 1884. 



Batostomella gracilis, Nicholson. 



Chsetetes gracilis, Nicholson, 1874, Quart. Journ. Geol. Soc. vol. 30, p. 504, pi. 29,. 



figs. 7-7a. 

 " " 1875, Pal. Ohio, vol. 2, p. 198, pi. 21, figs. 8-86. 



" " " 1876, Ann. and Mag. Nat. Hist., Ser. 4, vol. 28, p. 



90, pi. 5, fig. 13. 

 MoiiticuKpora {Heterotrypa) gracilis, Nicholson, 1881, genus Monticulipora , p. 125? 



fig. 20, and pi. 2, figs. 1-16. 



The typical form of this species is common at the tops of the hills 

 about Cincinnati, Ohio, where it is restricted to a vertical range of 

 about fifty feet. Nearly 300 feet higher in the series a slightly modified 

 form reappears, differing from the typical one mainly in having the 

 zooecial walls somewhat thicker than usual. This variety, if it may be 

 so called, has been found at Oxford, Ohio ; Richmond, Ind. ; Wilming- 

 ton, 111., and Spring Yalley, Minn., and at all of these localities it occurs 

 near the top of the Hudson River or Cincinnati group. Its geographical 

 range is now extended to Manitoba, as I have recognized several frag- 

 ments of it among the material collected at Stony Mountain, by Mr. 

 T. C. Weston in 1884. 



