APPENDIX. 



GENERA INCERTiE SEDIS. 



[The following genera cannot be satisfactorily referred to their proper places in 

 the system until their fruit shall have been discovered. Wurdemannia may perhaps 

 belong to Gelidiacece ; and Pikea, either to Sphcerococcoidece or to Ceramiacea;.] 



WURDEMANNIA. (Nov. Gen.) 



Frond filiform, terete, irregularly branched, composed of three strata ; the medul- 

 lary of numerous, slender, cylindrical, seriated cells, disposed in sub-parallel, closely 

 packed, longitudinal filaments ; the intermediate of oblong, longitudinal cells 

 gradually shorter towards the periphery, which consists of minute, vertical cellules, 

 in a nearly single row. Conceptades (unknown.) Teiraspores oblong, zonate, 

 immersed in the peripheric cells of the swollen apices of the branches. 



The little plant on which I venture to found the present genus has puzzled me a 

 good deal. In its aspect it resembles Caulaca7ithns, but has a structure more nearly 

 agreeing with that of Gelidium than of any other genus with which I have com- 

 pared it. From Gelidium, however, it difliers essentially in the zonate tetraspores. 

 I had at one time thought of placing it, provisionally, in Dicranema, but after hav- 

 ing consulted with ray friend Prof Agardh, who is equally unable with myself to 

 point out its true affinities, I have determined to propose it as the type of a new 

 genus, though its claims cannot be fully substantiated until the conceptades shall 

 be discovered. Meanwhile I inscribe it with the name of the late Dr. Wurdeman, 

 a most meritorious naturalist, who first explored the raai-ine botany of the Florida 

 Keys, and from whom (through Prof. Lewis R. Gibbes) I received specimens of 

 this plant, among many others. 



Owing to the tenuity of the frond, it is difficult to obtain a longitudinal section. 

 The structure above described has been ascertained by viewing small portions 

 which had been treated with muriatic acid, and then strongly pressed between 

 pieces of glass. 



