96 FLORA OF LOWER COAL MEASURES OF MISSOURI. 



collection are Nos. 3182, 3184, 3185, and 31iH, all of which show the 

 form and nervation, as well as the villosit}^, of Pecopteris cUutoni. 



Similarly, as might be siispected from a comparison of figs. 4 and 6 on 

 pi. xxvii in the Coal Flora, with figs. 4 and 6, respectively, of pi. xlii of the 

 same work, Nos. 3181 and 3183, the originals, respectively, of these figures, 

 fail, so far as I am able to discover, to present an Alethopteroid nervation, 

 and after a careful examination, being unable to discern the nervation 

 delineated by the artist, I do not hesitate to refer both of them to the 

 Pccopteris dintonl. 



An obscure fertile segment which seems referable to this species is 

 also present in the coMection. The flattened sporangia are generally oval, 

 often squarrose, or obovate-squarrose, and usually crowded on the surface 

 of the pinnule. Five, six, or seven are usually grouped in the sorus, the 

 arrangement being apparently about a short central column; but in many 

 cases in which the group contains seven or six sporangia, one of the latter 

 appears to occupy a central position. The cells of the sporangium wall, 

 which seems to open by a cleft extending downward from the apex, are 

 elongated in the direction of the longer axis of the sporangium. 



As has ah-eady been stated, the sporangia seen in the original of fig. 5 

 on ]il. xlii of the Coal Flora are, though obscure, probabl}?- of the type 

 found in connection with the Pecopteris pseudovestita, to which the some- 

 what erroneously delineated sterile portions of the specimen seem also 

 referable. 



Although Pecopteris dintoni presents rarely in the upper pinnae a form 

 similar to CaUipteridium memhranaceum Lx., it is easily distinguished by the 

 nervation when the latter is seen, as well as by the almost constantly pres- 

 ent villosity. In reality the general aspect of the pinna of this species is 

 Pecopteroid or slightly Sphenopteroid, quite in contrast to the Alethopteroid 

 phase of the Callipterkl'mm. Tlie pinnae of our species are considerably 

 larger, more obtuse, more irregular and lax than those of P. vestita, Avliile 

 the raehis is not punctate. The nervation also in P. clintoni is more distant 

 and generally more oblique. With P. pseudovestita P. dintoni is not likely 

 to be confused, on account of the greater size, more oj^en arrangement of 

 the pinna?, the miich larger, decurrent, polymorphous, tapering, villous pin- 

 nules, the distant tine, relatively straight, very oblique, and jnore simple 

 nerves, and the much smaller and more rounded sporangia in the latter. 



