﻿American Palceozoic Fossils. 



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external characters. Sections of the two forms, however, show con- 

 clusively that they are widely different, as will be seen by comparing 

 figs, lb and 7c with 8 and 8a, on Plate I. 



Formation and locality: A characteristic fossil of the Kaskaskia 

 Group of the Lower Carboniferous rocks. My types are from Chester, 

 111., and Tateville, Ky. 



Rhombopora pulchella, n. sp. (PI. I., figs. 6, 6a.) 



This species resembles the preceding so much that a detailed 

 description is scarcely necessaiy, and I will only point out the prin- 

 cipal external points of difference between them. Its branches, while 

 they are of the same size as those of JR. persimilis, differ in their 

 mode of branching, as they divide dichotomously. The cell aper- 

 tures are, if at all different in size, slightly larger and more acute 

 above. The vestibules are narrower, and extend considerably beyond 

 the front end of the aperture, where they enclose a rounded node or 

 spine, which is situated just in front of the aperture. The margins 

 of the vestibules are not sharp as those of that species, and carry 

 two, sometimes three, rows of minute granules. At irregular intervals 

 one of the zocecia is missing, the vacant spot in that case being 

 occupied by a small aggregation of spines or granules. 



The peculiarities are all brought out in fig. 6a, on Plate I., repre- 

 senting an enlargement of the surface of a branch to 18 diameters. 



Formation and locality: Rather rare in the Kaskaskia Group of the 

 Lower Carboniferous, at Tateville, Ky. 



Rhombopora armata, n. sp. (PI. I., figs. 5, 5a.) 



Zoarium ramose, branching very much like B. persimilis. Zocecia 

 with deep but narrow vestibules, and comparatively large sub-circular 

 apertures, arranged regularly in a quincuncial manner, forming there- 

 fore vertical; transverse and obliquel}' intersecting series. Between the 

 ends of the cells are found, almost invariably, two large and remarkably 

 prominent spines, which, except, in perfectly cleaned examples, thor- 

 oughly obscure the zocecial apertures. Under the common pocket 

 lens these spines seem to b. more especially arranged in transverse 

 series, but by viewing them from different points they also arrange 

 themselves in oblique and vertical series. Measuring transversely, six 

 cells occupy the space of 0.05 of an inch, and eleven to thirteen encircle 

 the branch; vertically, seven occur in 0.1 inch, and obliquely, about 

 twelve occupy the same space. 



