364 Systematic Paleontolo.gy 



appears to have been wide and ribbon-like, but this was not the case. 

 The segments are inserted on the upper surface of the rachis in conform- 

 ity with the generic diagnosis, and in one of the larger specimens .(an 

 impression on the reverse side of the specimen shown on pi. Ivii), the 

 lateral veins of opposite sides approach to within 1 mm. of each other, 

 being separated by a slightly raised ridge. Below it is seen that the 

 rachis is flattened, and during or since fossilization, small fragments 

 of the inner margin of the segments overlying the rachis have flaked 

 off, exposing more or less of the broadly flattened rachis below as is well 

 shown on pi. Iviii. Fig. 1 shows a diagrammatical cross-section of this 

 frond. 



In pi. Ivii, fig. 2, the appearance is somewhat different, due entirely 

 to the process of fossilization. The right hand segments are in place, 

 attached to the upper raised line of the rachis, which during fossilization, 

 possibly by the creep of the strata before lithification, was laid over 

 toward the left and flattened, the left hand segments being detached and 

 superimposed upon the flattened rachis. Text-fig. 11a is a diagram- 

 matical cross-section across the base of this specimen. 



Eemains very suggestive of this species, but in a more fragmentary- 

 condition, have been described by ISTathorst from an unknown, probably 

 N'eocomian, locality in Japan as Macrotceniopteris (?) marginata.^ 



Occurrence. — Patuxeistt Formation. Fredericksburg, Virginia. 

 Arundel Formation. Langdon, District of Columbia. 



Collection. — U. S. jSFational Museum. 



DICHOTOZAMITES gen. nov. 

 Fronds dichotomously compound. Rachis relatively slender, keeled. 

 Pinnules slender, linear, acuminate, ascending, with a markedly decur- 

 rent base, attached laterally, alternate to opposite. Margins simple 

 tending to be slightly inroUed dorsally. Venation consisting of a single 

 midvein to each pinnule, prominent below and slightly sunken above, 



^Nathorst, Beitr. z. Mesozoisclieii Fl. Japans, Denks. k. Akad. Wiss. Wien, 

 Band Ivii, 1890, p. 54, pi. vi, figs. 6, 6a. 



