DliSCRlPTIOX OF THE SPECIES. 257 



crowded twigs. It is much the most common conifer at Wliite House, 

 where it seems to have been abundant. Owing, however, to the friable 

 nature of the chTV which contains t]ie imprints and its acbnixture witli sand 

 the specimens are poorl}- preserved. Tlie specimen figured was evidently 

 a very large form originally. When found it extended over five or six 

 inches of area, but was broken in taking it up. 



SPHENOLEPIDIUM, Ileer (SPHENOLEPIS Schenk). 



Branches and twigs alternate, with spii-ally placed, short, imbricated 

 leaves that are decurrent at base, acute or acuminate on the younger 

 twigs, appressed on the older ones, divergent and somewhat curved in- 

 wards ; cones placed on axillary lateral branchlets which have close 

 appressed leaves and form a raceme, persistent, rounded, or oblong ; scales 

 of the cones persistent, leathery, wedge-shaped, with the ujjper margin 

 ti'uncate, when mature, divergent. 



This description of the genus by Schenk applies veiy nearly to a 

 number of coniferous plants from the Potomac flora, which, with the species 

 of Taxodlum, form very important elements in this flora. These two genera 

 usually are to be found associated together at the same localities and in 

 the same layers, and with them we usually find some of the species of 

 Sequoia. The constant association of the forms of these three genera is no 

 doubt due to the accidents of preservation, the conditions favoring the 

 preservation of one promoting likewise that of the others. It is possible 

 that some of these plants may really belong to that group of Sequoias that 

 possesses imbricated scale-shaped leaves, such as »S'. concinna, etc. In the 

 absence of fructification the question can not be positively decided. Cer- 

 tainly these plants possess in the forms of the leaves and twigs many 

 features seen in that section of the Sequoias. 



Sphenolepidium paeceramosum, sp. nov. 



Plate CXXIX, Fig. 7 ; Plate CXXX, Fig. 8 ; Plato CXXXI, Fig. 2. 



Branches long and slender, dividing at long intervals in a dichotomous 

 manner, giving a few rather stout, long, cylindrical branches, showing a 

 tendency to fastigiate grouping; lateral leaves short, acute, with a distinct 

 MON XV — 17 



