596 NEW YORK STATE MUSEUM 



Thamnocladus clarkei sp. nov. 



PI. 3, fig. 1; pi. 4, fig. 1, 2 



Fronds spreading, densely ramons, lax, pinnately and some- 

 what regularly dicbotomous, intricate by reason of tbe repeated 

 asymmetric divisions at intervals of 5-20mm; lamina relatively 

 narrow, l-7mm broad, thickest at the base, probably oval or 

 subcylindric in section, narrowed slightly in each subdivision, 

 the borders parallel, forking at a moderate or wide angle, and 

 slightly recurved above each bifurcation, producing a graceful 

 subflexuous form; central axis or strand slender, median or 

 nearly so in the impressions, generally parallel to the borders, 

 forking at a narrow angle a little below each dichotomy of the 

 frond, tapering gradually upward, generally discernible through- 

 out the greater portion of the flattened or macerated impressions, 

 though often obscure in the basal portions or terete fragments. 



One of the more important as well as conspicuous characters 

 of Thamnocladus clarkei is its mode of division with a 

 regularity and relative symmetry which, combined with the 

 slightly divaricate attitude of the branchlets, results in a grace- 

 ful flexuosity. The details of this habit which may be noted in 

 the slender branches on the right on pi. 3 and pi. 4,fig. 1, are still 

 more clearly seen in two isolated branches on a small slab^ from 

 Meshoppen Pa., shown on pi. 4, fig. 2. The more delicate segment 

 in the latter beautifully illustrates the characteristic bifurca- 

 tion and the gradual narrowing of the lamina with each succes- 

 sive subdivision. The width of the ultimate lobes is nearly the 

 same, about 1mm, in all the examples. The Meshoppen speci- 

 mens also indicate rapid sedimentation, since the lower portion 

 of the fragment on the left completely traverses the slab, over 

 1cm thick, in an oblique direction. Its downward continuation 

 was in lower strata. The central strand, while slightly clearer 

 in the better preserved Meshoppen fragments is in precise agree- 

 ment with the fronds from East Windsor. 



The substance of the lamina in all the specimens has been re- 

 duced to a compressed carbonaceous residue which is mostly re- 



^No. 25072 of the Lacoe collection, United States national museum. 



