DESCRirTlON OF SPECIES— CEYPTOGAMIA—ALGJ5. 37 



Tuck., of Texas. It is also more distantly comparable to Graphis elegans, 

 Nyl., of Oahu. 



HABiTAT.^-Black Butte ; upon a piece of clay shale, the counterpart or 

 impression of a stem of Caulinites sparganioides. 



ALG^. 



As for the Lichens, the exact determination of the fossil remains of 

 marine plants generally named Fucoids is not possible. Their forms, however, 

 are sometimes definable, and persistent also ; and thus, if all their characters 

 are not positively determinable, and if even their generic references are mostly 

 uncertain, they may be at least compared, separated in groups under definite 

 names, and used for the identification of geological formations. Still for 

 this, they are not as reliable as land plants. Their types appear to be 

 preserved for long space of time, on account of the slow modifications of the 

 element wherein they live. Hence we find some species present in two 

 formations whose age is indicated as different by the remains of land plants. 

 The study of the fossil Algce is also rendered difficult by their distribution 

 in series of rocks, especially of sandstone, of some thickness. Growing up 

 as fast as the sand is heaped around and covers them, they send their branches 

 in every direction, sometimes filling the rocks by their multiple subdivisions 

 in such a way that even large specimens do not represent the characters of 

 their general outlines. The most of the Alg<B are moreover of a soft sub- 

 stance, easily destroyed by decomposition, and then flattened and mixed 

 together in an amorphous mass. Their former existence is often recog- 

 nized only by flakes of carbonaceous matter, or even by the mere discoloration 

 of the rocks. Heavy beds of sandstone in New Mexico and Colorado, 

 especially, contain a profusion of fossil remains of Algce, and if it had been 

 possible either to cut them from the rocks or to study and to figure them in 

 place, a large number of very diversified forms could have been represented 



and described here. 



HALYMENITES, Sternb. 



Ilalymciiitcs striatiis, Lesqx. 



Plate I, Fig. 6. 



Halymenites atriahis, Lesqx., Annual Report, 1872, p. 373. 



Frond large, dichotomons, erect; branches short, obtuse, cylindrical, or more or less flattened by 

 compression; surface irregularly striate. 



This species is related to the following by its ramification, whicli is 

 extremely variable. Sonietimes the branches on a more or less obtuse angle 



