606 PALEONTOLOGY OF ILLINOIS. 



fenestrules oval, nearly or quite as wide as the branches, eight 

 in 1 cm. The zooecia have prominent mouths, with twenty or 

 twenty-one in 5 mm. The variety thus appears to be more 

 compact in every way than the typical form. 



Position and locality: St. Louis group and Warsaw beds. St. 

 Louis and Barrett's Station, Mo. Alton, Columbia, Warsaw 

 and localities in Monroe Co., 111. The variety is from Elizabeth- 

 town, Ky., where it was found associated with typical St. Louis 

 fossils. 



THAMNISCUS King, 1849. 



(Ann. & Mag. Nat. Hist. 2d ser., Vol. III. p. 389.) 

 (For generic diagnosis, see page 397.) 



This genus was founded by King upon the Permian fossil 

 Keratophytes dubius Schlotheim. It also seems evident that 

 King intended to include Silurian and other forms as well, but 

 to arrive at a true and conclusive idea of the genus the char- 

 acters of the type species alone can be depended upon. 



King's description of T. dubius has been shown to the errone- 

 ous in several important respects by Mr. G. W. Shrubsole.* 

 He shows that the supposed "gemmuliferous vehicles," only re- 

 present the broken or worn hollow spines, and that the zooecia 

 apertures are provided with an elevated peristome. These ob- 

 servations I can verify, having lately studied a series of German 

 specimens which were procured for the purpose. I find, further, 

 that the poriferous face of the branches is in every essential 

 respect identical with that of such species of Polypora as P. 

 cestriensis and P. spinulifera. Some of my own specimens 

 being in a good state of preservation show the nodes or spines 

 and the peristomes very well, and that the latter are especially 

 prominent about the apertures of the marginal zooecia,. The 

 nodes are numerous and occur on two or three faint longitudi- 

 nal lines which run between the ranges of apertures. Another 

 character that aids in linking the genus to Polypora is shown 

 by the two specimens figured on plate 62. There is an occa- 

 sional dissepiment, which unites the branches when, after bifur- 



* Quart. Jour. Geol. Soc. for Aug., 1882, p. 341. 



