526 PALAEONTOLOGY OF ILLINOIS. 



PACHYDICTYA FENESTELLIFORMIS Nicholson. 



PI. XXXI, fig. 1. 



Ptilodictya fenestelliformis Nieh., 1875. Ann. & Mag. Nat. Hist. 4 ser. Vol. 5, p. 181. 

 PI. XIV, fig. 5-5b. 



Ptilodictya fenestelVformis Nich., 1875. Pal. Ohio, Vol. II, p. 263, PL XXV, figs. 8, 8b. 



Ptilodictya fenestelliformis Nich., 1875. Kept. Pal. Ontario, p. 14. 



Phcenopora fenestelliformis Ulrich, 1882. Jour. Gin. Soc. Nat. Hist. Vol. V,P1. VIII, fig. 8. 



This species is exceedingly abundant at Wilmington, 111. Its 

 ramose habit of growth and comparatively small branches dis- 

 tinguishes it from the four species of the genus with which it is 

 associated, one of them still undescribed. 



The figure represents a small but nearly complete example of 

 a variety which I propose to call corticula, from the fact that 

 the zooecia apertures of the lower half or more of the zoarium 

 are covered by a more or less thick, and finely granulose or 

 striate, solid deposit. The zoarium of the variety is larger and 

 the branches wider and much stronger than in the typical form. 

 In both the surface exhibits sometimes conspicuous, at the other 

 times faintly defined smooth spots. The zooecia apertures are 

 small, widely separated, surrounded by a peristome, ranged in 

 longitudinal rows, with twelve or thirteen in 5 mm. The inter- 

 nal structure is similar to that of P. gigantea. 



P. fenestelliformis and its var. corticula, belong to a group 

 of closely related species, comprising, besides, P. acuta Hall and 

 P. occidentalis Ulr., from the Trenton, and P. biturcata VanCleve 

 (Hall) and P. turgida Foerste, from the Clinton. 



Position and locality: Cincinnati group, Wilmington, 111. 



EUSPILOPORA Ulrich. 



(For generic diagnosis see page 389.) 



EUSPILOPORA SERRATA Ulrich. 



PI. XLIII, fig. 4-4h. 



Zoarium a narrow stipe, branching dichotomously as a, rule, 

 with serrate margins, width about two mm., thickness 0.8 mm. 



