CHARACTERS OP TRIBES AND GENERA. 169 



Jamesonia cannot be considered otherwise than a truly 

 aberrant genus ; according to my view its nearest relation- 

 ship appears to be with Gymno gramma, and its revolute 

 indusaeform margin seems to warrant its being placed in the 

 present section. 



78. PLECOSORUS, Fee (1851). 

 Cheilanthes sp. Hook. Sp. Fit. 



Vernation fasciculate, erect, acaulose. Fronds stipate, 

 lanceolate, li to 3 feet high, bi-tripinnatifid, densely pilo- 

 squamose ; pinnas numerous, contiguous, sessile, linear 

 lanceolate, 4 to 6 inches long ; pinnules oblong lanceolate, 

 5 to | of an inch long, laciniately lobed, lobes small, 

 margins inflexed, forming cucullate scariose universal 

 indusia. Veins forked, obscure ; venules free. Sporangia 

 sub-terminal. Sori punctiform, contiguous, included under 

 the cucullate indusia, ultimately confluent. 



Type. Cheilanthes speciosissima, A. Braun. 



Illust. Fee Gen. Fil., t. 13, fig. 1; Moore Ind. Fil., 

 p. 28, A. 



OBS. This genus is founded on a solitary species, a 

 native of Mexico. It is a Fern of peculiar aspect, pos- 

 sessing characters that makes its relationship doubtful. 

 The multifid and squamose fronds point towards Notho- 

 chloena and Cheilanthes, but from which it differs in having 

 lateral, intramarginal sori, which are involved in numerous 

 hair-like scales, and which, being included under the indu- 

 sesform margin, seems to indicate its affinity with Allosorus ; 

 under these circumstances I deem it best to place it in the 

 present section in proximity to Jamesonia. 



Sp. P. speciosissima, Moore (P. mexicana, Fee; Cheilanthes 

 speciosissima, Kze. Analct., t. 23). 



