392 



PALEONTOLOGY OF ILLINOIS. 



CLATHROPORA Hall. Zoaria composed of anastomosing 

 branches, forming a regular net-work with round f,:iestrules. 

 Minute structure essentially the same as in Ptilodictya,. 



Type: C. frondosa Hall. Range (?) Trenton to Upper Hel- 

 derberg. 



PILENOPORA Hall. Zoaria as in Ptilodictya, from which they 

 differ in having two mesopores between the ends of the zooecia 

 apertures. 



Type: P. explamitn Hall. Range, Cincinnati to Lower Hel- 

 derberg. 



0- V 



Fig. 12. Sections illustrating the internal structure of Phcenopora; allx25. a, tangen- 

 tial section of P. constellata Hall, showing structure of zoarium just beneath the sur- 

 face; l>, half of a vertical section of same; c, deep tangential section of P. expansa H. & 

 W., showing structure of zoarium just above the median laminae; d, tangential section 

 of P. lindstromi n. sp., showing the pitted margin and three rows of zocecia; e, vertical 

 section of same.* 



* Phasnopora lindstromi is from the Upper Silurian deposits of Gotland. It grows 

 into narrow, parallel-margined, compressed branches, about 1.5 mm., thick, 3.8 to 4.5 

 mm. wide, bifurcating at intervals of 10 mm. more or less. Margins wide, rather 

 sharp, with several rows of small pits. Zocecia apertures elliptical, about 0.19 mm. long, 

 arranged in 9 to 12 longitudinal series, 14 in 5 mm. Between the ends of the apertures 

 are the usual two mesopores. 



I am indebted to the eminent palaeontologist, Dr. Gustav Lindstrom, of Stockholm, 

 Sweden, for an excellent example. 



