640 PALAEONTOLOGY OF ILLINOIS. 



ences, and in having three instead of two rows of zooecia. In 

 the length and form of the fenestrules the species resembles P. 

 trentonensis Nich., but they differ too obviously in other re- 

 spects to require any further comparison 



Position and locality: (?) Base of Cincinnati group, Alexander 

 Co., 111. Another specimen was collected by Prof. Moritz Fischer 

 in the upper beds of the Trenton group at Lexington, Ky. 



CHAINODICTYON Foerste, 1887. 



(Bull. Sci. Labor. Denison Univ., Vol. II, p. 81.) 

 (For generic diagnosis see page 399.) 



This genus was founded upon a species from the Lower Coal 

 Measures of Ohio. Its fenestrules and zooecia apertures are 

 slightly larger than those of the Illinois form, but in all other 

 respects the two agree very closely. Both greatly resemble the 

 Retepora, undata McCoy, in having the reverse transversely un- 

 dulated, and it is not improbable that a careful examination of 

 McCoy's species will show it to be congeneric with the American 

 types. The elongate, conical, or subtubular zooecia, their large 

 impressed apertures, and the thin interspaces, place the genus 

 into the new family PHYLLOPORINIDJE. 



CHAINODICTYON LAXUM var. MINOR Ulrich. 



PL LXII, fie. 3-3a. 



Zoarium a reticulated foliar expansion, consisting of thin in- 

 osculating branches, united in such a manner that they leave 

 irregular lozenge-shaped fenestrules averaging 1.5 mm. in length 

 by 0.8 mm. in width. The fenestrules are ranged in moderately 

 regular longitudinal and diagonally intersecting series, with re- 

 spectively 4.5 and 6 to 7 in 1 cm. each w r ay. Branches strongly 

 convex on the obverse side, 0.3 to 0.45 mm. in width, with four 

 alternating ranges of zooecia. Apertures rather large, ovate- 

 acuminate, somewhat oblique, arranged in acute diagonal series. 

 On the reverse face the branches are marked with sub-imbricat- 

 ing transverse folds or striae, which pass across the flattened 

 surface of the branches in a curved direction. 



