338 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



centrifugal and continuous portions characterized forms which passed 

 by gradations into the Cycadophytes. Scott and Solms Laubach, on 

 the other band, regard the Medullosaceae as a highly differentiated 

 derivative of a Heterangiumlike ancestor which became so specialized 

 that it became extinct during the Permian. Other genera that 

 appear to belong to this family are Colpoxylon, Rhexoxylon, and pos- 

 sibly Steloxylon, all based upon fragments of petrified stems from the 

 Paleozoic of Europe, Africa, and Asia. 



Medullosa petioles are referred to the genus Myeloxylon and 

 structural material has been described from both Europe and Amer- 

 ica. The foliage of Medullosa was of the frond types known as 

 Neuropteris, Alethopteris, and Linopteris ; all of which were exceed- 

 ingly abundant and cosmopolitan in the later Paleozoic floras. Im- 

 pressions from the Scotch Carboniferous show large Rhabdocarpus 

 seeds attached to the fronds of Neuropteris tteterophyUa and similar 

 but still larger seeds attached to Belgian specimens of Neuropteris 

 obliqua. N. Schlehani and N. auriculata have also been shown to have 

 been seed-bearing. 



The microsporangia appear to have been four valved and termi- 

 nal on naked pedicels in A. heterophylld or marginal on orbicular 

 or cuneate pinnules as in Potoniea, N. gigantea- and N. Carpentieri. 

 Although no seeds have been found in actual connection with Alethop- 

 teris there are good reasons for believing that some species at least 

 (e. g., A. lonchitica, A. Serlii) bore seeds of the Trigonocarpus type. 

 The latter, which are often exceedingly common as impressions and 

 casts, as described from petrified material are elongate-oval radially 

 symmetrical. The testa is thick and consists of an outer flesh (sar- 

 cotesta) a shell (sclerotesta) and an inner flesh. The shell has 

 three longitudinal ribs which characterize the seeds when preserved 

 as casts after the decay of the outer flesh. Less prominent lines are 

 intercalated between the main ribs. There was a long triangular 

 micropylar canal leading to a small pollen chamber in the apex of 

 the nucellus and the latter is free to the base. 



Other genera that may represent sporangia of different types of 

 Medullosaceae are Codonotheca, Schiitzia, Whittleseya, Dolerophyl- 

 lum, and Ottokaria ( ?). 



The bulk of the remaining types referred to the Pteridospermo- 

 phyta are based upon anatomical studies of stem or petiole frag- 

 ments ranging in age from the Devonian (Kalymma) to the Permian 

 and will not be described in the present connection. In addition to 

 these, several types of fronds formerly referred to the ferns have 

 been proved to be seed-bearing, as, for instance, fronds referred to 

 Pecopteris Pluckeneti but probably representing P. Sterzeli, in which 

 (he slightly reduced pinnules bore terminal oval seeds with a thick 



