54 FLOEA OF LOWER COAL MEASURES OF MISSOURI. 



small pinnules, the decurrent sinuses between the latter gradually approach- 

 ing the rachis but not reaching it; lamina rather thick, rugose, often arched 

 between the nervils, and usually somewhat repand, so as to conceal the 

 teeth in the matrix; nervation generally clear, the primary nerve strong, 

 originating at a moderate angle, but slightly if at all decun-ent, slightly 

 subgeuiculate near the top, forking pinnatel}'' at a rather open angle at the 

 base of each lobe, each secondary nerve in the pinnatifid pinnules forking 

 pimiately again in the middle portion of the lobe to furnish one oblique 

 upward-turning nervil, which passes to the apex of each tooth. 



One of the most common species in the flora of the Coal Measures 

 about Clinton is that described by Lesquereux in the first volume of the 

 Coal Flora as Sphenopteris Brittsii. Fragments of this species are found 

 scattered over a large proportion of the slabs, and, although its surface is 

 rugose and irregular, often ragged in appearance, the slender sinuous pinnae 

 are frequently pleasing- in general eft'ect. 



The semblance of a smooth margin in the lobes of many examples is 

 due to a slight convexity of the pinnules and the consequent concealment 

 of the teeth in the matrix, and is not really so frequent nor so complete as 

 mio-ht be inferred from the figure in the Coal Flora. On this account I 

 have sought to represent, by photo-reproduction, figures of portions which 

 will show the margin as well as several phases in the development of the 

 pinhfe. The margins are decurrent in the specimen figured by Lesquereux, 

 as well as in ours. The former also shows the punctate rachis, often slen- 

 der or somewhat geniculate. The punctations on the stem are found to be 

 the basal scars of short spines. The compound pinnules are always decur- 

 rent, bordering the racliis with a narrow wing. Very rarely, when the 

 margins are broken away or concealed, the most slender pinnae of Sphenop- 

 teris Brittsii resemble 8. mixta Schimper, but even in these attenuated pinnae 

 the species can be readily distinguished by the more rugose, coriaceous 

 texture, the uneven surface of the limb, the much stronger rachis, densely 

 punctate, the broad, compact pinnules, the more ovate lobes, the straighter 

 pinnae, and the dentition, seen even in the earliest stage of the division. 



Sphenopteris Brittsii Lx. belongs naturally to the section of the Sphe- 

 nopterids represented by S. chcerophylloides Brongn., or ^S". cristata Brongn., 

 which Potonie^ separates as a distinct genus, Ovopteris. Our specimens 



' Fl. Rothl. Thiiringen, p. 44. 



