Sellards — Fronds of Crossotheca and Myriotheca. 197 



Crossotheca sagitiata preserves the details of fractification 

 much better than the other American species, and illustrates 

 well the characters of the genus. The large fertile pinnules 

 are expanded at the base in the form of an arrow, thus allow- 

 ing greater area for the attachment of the sporangia. The 

 small pinnules are slightly or not at all enlarged at the base. 

 The upper surface of the pinnule is flat with a distinct median 

 line, and with the lateral veins obscured. The sporangia are 

 unusually large, measuring 24- to 4™°" in length and ^ to f"^"^ 

 wide. They are placed as seen in figures 1 , 2, and 8, in a single 

 row around the entire border of the pinnule, free nearly or 

 quite to the base, and are often seen filled with spores. 



Figure 2 gives a side view of the pinnule as partly freed 

 from the matrix, and showing the full length of the sporangia. 



From a study of the type of the genus, Prof. Zeiller thought 

 it probable that the sporangia were united in little clusters at 

 the ends of the nerves. The specimens figured and others in 

 the Yale collection indicate that in the case of C. sagittata^ at 

 least, the sporangia are attached side by side in a single row, 

 without any tendency toward grouping. The same specimens 

 confirm the statements of Zeiller that these are individual spo- 

 rangia, since, in the specimens at hand, they are often filled 

 with spores, in contradistinction to Stur's interpretation of the 

 fringed pinnules as dehisced sporocarps..* 



Some of the best preserved sporangia show a slit on the 

 outer side, as seen in figure 3^, which probably indicates the 

 place of dehiscence. • 



The sterile part of the frond is very different from the fer- 

 tile, so much so that if not found in direct connection their 

 relation would hardly be suspected. The pinnules are small, 

 rounded, close, oblique, connate, and decurrent at the base, the 

 smaller entire, the larger becoming lobate. The ultimate 

 pinnae are broadly linear-lanceolate, alternate, oblique, and 

 close, often touching. The rachis is large and round. The 

 midrib of the pinnule is broad, shallow, and decurrent. The 

 lateral veins curve regularly to the border, and fork once, 

 twice, or three times, according to the size of the pinnule. 

 The surface is rough, appearing minutely scaly. Some of the 

 veins are heavier than others, giving the venation an irregular 

 appearance. 



The extreme apex of the frond is often sterile, the fertile 

 pinnules and pinnae appearing at some distance below. This 

 is not always the case, however, since in the frond figured by 

 Lesquereux (" Coal Flora," volume iii, pi. C, figure 4) the entire 

 apical part is fertile. It is not possible to state, on any evi- 



*Ab'handl. d, k. k. Geol. Eeichsanstalt, Wien, 1885-87, Flora der Schatz- 

 laren Schichten, Part I, pp. 273-275. 



