620 PALEONTOLOGY OF ILLINOIS. 



so arranged that one is always opposite a pinna, and one in 

 the space between. 



This species is closely allied to the P. flexicarinata (Y. & Y. 

 sp.) from the Carboniferous shales of Scotland. A comparison 

 with authentic examples of that species shows that the Scotch 

 form has six pinnae to 5 in this; and fourteen cell apertures to 

 twelve in P. bellula. The carina, nodes, and granulose striae of 

 the reverse are also all stronger than in the Illinois form. The 

 P. whitei Foerste, from an equivalent horizon in Ohio, differs 

 chiefly in having seventeen cell apertures where P. bellula has 

 only twelve. 



Position and locality: Base of Coal Measures; Seville, 111. 



PlNNATOPORA TRILINEATA Meek. 



PL LXVI, fig. 6. 

 Glauconome trilineata Meek, 1872. Pal. East Neb. p. 157. PI. 7. flg. 4aV 4b-4d. 



Zoarium a pinnate frond, the primary midrib 0.45 to 0.6 mm. 

 wide, giving off long secondary lateral midribs, 0.35 to 0.45 

 mm. wide, at intervals of 3 mm. or more. Pinnae 1.5 to 2 mm. 

 long, 0.3 mm. wide, nearly opposite, twelve on each side in 1 

 cm. Reverse face strongly rounded, distinctly marked with 

 longitudinal striae, those on the pinnae finer than those on the 

 midribs. Obverse face of midribs subangular, with three, fine, 

 straight lines along the center, the median one slightly the 

 strongest. Pinnae similarly marked but on a smaller scale. 

 Zocecia and their apertures in two ranges in both midrib and 

 pinnae. Apertures circular, 0.09 mm. in diameter, about 

 twice as far apart longitudinally, with seventeen in 5 mm.; so 

 arranged that one occurs opposite the upper half of the base of 

 each pinna, and two in the space between. When in a good 

 state of preservation they are surrounded by a thin and sharply 

 elevated peristome. Of internal characters the strong develop- 

 ment of hemisepta is the most noteworthy. 



The three mesial lines constitute the principal external peculi- 

 arity of this species. 



According to Meek's measurements, between eight and nine 

 pinnae are given off on each side in 1 cm. I have examined per- 

 haps one-hundred fragments and all give twelve in that space. 



