/Sellards — Validity of Idiojyhyllum rotimdifolium. 203 



Aet. XXIII. — On the Validity of IdiojjhyUum rotimdifolium 

 Lesquereux^ a Fossil Plant from the Coal Measures at 

 Mazon Creek^ Illinois; by E. H. Sellards. 



The genus Idiophyllum was proposed by Lesquereiix for a 

 species of Carboniferous plants represented by a single speci- 

 men from Mazon Creek, Illinois.^ 



The species I. rotundifolium appeared to present characters 

 so peculiar that the genus was placed by Lesquereux in his 

 classification with the " Ferns of IJncertain Relation," and was 

 compared with Dictyophyllum^ and with dicotyledonous leaves. 



Figure 1. — Obverse of the type of Idiophyllum rotundifolium Lesqx. 



In working over a large collection of plants from the same 

 locality, in the Yale Museum, the writer has found the obverse 

 side of Lesquereux's type. The obverse (figure 1) is well pre- 

 served, and completely demonstrates the true nature of the 

 plant. The fossil represents the distorted apical part of a young 

 and not fully expanded fern frond. The tip is pushed to one side, 

 crowding the lateral pinn?e and partly obscuring the outline of 

 the pinnules. The pinnules, however, are much more distinct 

 than is represented in Lesquereux's figure of the counterpart. 

 They are 6 to lO'"'" in length, 3 to 3^™"^ in width, alternate, 

 obtuse, and somewhat cordate at the basal attachment. The 

 rachis is longitudinally striate ; the lateral pinnae are close, 

 oblique, and alternate. In all these characters Idiophyllum 

 rotimdifolium agrees with Neuropteris rarinervis Eunb., a 



* Second Geol. Surv. Penn., Description of the Coal Flora, vol. i. p. 159 ; 

 Atlas, pi. xxiii, fig. 11, 1880. 



