WHITE.] NOTES ON CHARACTERISTIC SPECIES. 875 



rounded, blending- into the ruther long' terminal, which often has its 

 obscurely sublobate or sinuate margins rolled back so as to make it 

 appear acute or even muricate; lamina of the pinnules not ver}^ thick, 

 dull, becoming" decurrent in a very narrow wing along the rachis. 



Nervation rather strong, distinct; primary nerve originating low 

 at an acute angle, arching outward, not rigid, forking repeatedly 

 at a moderately wide angle; nervils a little distant, forking one to 

 three times and curving more or less in passing, with diminishing- dis- 

 tinctness, to the margin. 



The examination' of the collections from the geological sections of 

 the Pottsville series, from Pottsville in Penns3dvania to the southern 

 extremity of the Appalachian coal field in Alabama, shows the species 

 described above, with its minor variations, to be one of the most ubiq- 

 uitous as well as the earliest American representatives of the genus 

 Marioptei'is. Under the name Pmudopecopteris murieata (Schloth.) 

 Lx., it has long been known in the collections from the whetstone beds 

 of Indiana, the Dade coal (Lookout sandstone of Hayes) in Georgia 

 and various points in Alabama. Recent studies in the field show it 

 to be specially prevalent in the middle division of the Pottsville series, 

 to which I have given the name Horsepen group. It is more particu- 

 larly characteristic of the upper part of this group. 



The ordinary ultimate divisions of Mariopterls potUvillea^ such as 

 are illustrated in PI. CXC, Fig. -I, are clearly characterized (1) by the 

 comparative remoteness of the pinna? and pinnules; (2) by the form of the 

 pinnules, which are broadly ovate, obtuse or obtuseh' rounded at the 

 apex, dilated above the base, and plainly constricted at the base, and 

 arched ventrally ; (3) by the large size of the pinnides, which is greater 

 than any of the earlier round-ovate, inflated-pinnuled forms yet found 

 in what may for convenience be called the Mariopteris nmricata group; 

 and, finally, by (4) the rather coarse, distinct, curved, rather close 

 nervation, which approaches near to that of Mariopterk tennesseeaiia^ 

 a form intermediate between J/, pottsvillea and M. murieata or M. 

 nervosa. 



The present status of Filiciten muricatus Schlotheim,' or of the 

 types of Brongniart's Pecopteris murieata^ seems slightly ambiguous, 

 since the /"*. murieata has latterly been united by Zeiller^ and other 

 European palco])otanists with ^Larwpterh nervom (Brongn.) ZeilL. a 

 form quite distinct from the American material hitherto recognized as 

 Schlotheim's species. 



It is true that the difference between the forms originally described 

 under the two names is much less than ^\■e have been led to believe 

 from the American interpretations of the illustrations and figures. 



' Petrefactenk., p. 409; Flora d. Vorwelt, pi. xii, figs. 21, 23. 

 "Hist. vi'g. fo.s.s.. Vol. I, p. :i52, pi. xcv, fig. 34; pi. xcvii, fig. 1. 

 ^ Fl. Foss. bassia houill. Valenciennes, p. 173. 



