598 NEW YORK STATE MUSEUM 



lamina, and the absence of the fernlike pinnate ramification 

 along a rhachis found in the latter genus. Psilophyton is vas- 

 cular and more or less distinctly fernlike in habit. Thamno- 

 cladus is as distinctly algoid in form. 



Among the living algae there are numerous species in various 

 families which present a more or less close superficial resem- 

 blance to the plants described above. So far, however, as the 

 external characters, to which our knowledge is at present con- 

 fined, are concerned the greatest similarity appears to be with 

 the Fucaeeae, though our plant also suggests some of the Dictyo- 

 taceae, specially Haliseriis delicatula. It may be com- 

 pared also with the red alga Stenogramma interrupt a 

 Mont. 



The material in hand appears to contain but little to indi- 

 cate a probable relationship of the supposed seaweed to the 

 orders of living algae. With respect to its habit and the aspect 

 of its more or less macerated lamina the closest analogies 

 would seem to be in the fucaceous Phaeophyceae, though the 

 possibility of a relationship with the higher types of Chloro- 

 phyceae should be kept in mind. Both of these great orders, 

 together with the red algae (Ehodophyceae) appear with little 

 doubt to have been represented by early types in the Devonic or 

 still older formations. 



The fossils of the species here described as T h a m n o c 1 a - 

 dus clarkei have generally been recorded in American 

 literature under the name Haliserites dechenianus 

 Gopp., to which the Meshoppen specimens shown in pi. D and 

 their associates were referred by Lesquereux. The identifica- 

 tion with the latter species is based on the original figures 

 and description given by Goppert 1 in his great work on the 

 Flora of the Transition series. The specific identity of the plant 

 described above with a portion of the Old World material 

 identified by various authors as H. dechenianus is pos- 



1 Fossile Flora des TJebergangsgebirges. Nova Acta Acad. C. L.-C. Nat. 

 Our. Sup. v. 22, Breslau and Bonn 1852, p. 88, pi. 2, fig. 1-6. First 

 named in N. Jahrb. f. Min. 1847. p. 686. 



