﻿DESCRIPTION OF PLATES. 281 



Plate XLV. P>isporan°;iate Strobili of Cycadeoidea. (1) Preserved 

 as an impression on a flat slab; (2-4) silicified entire. 



Photograph 1. — Cycadocephalus Sewardi Nathorst (103). 1, Natural size. Supple- 

 mentary figures Ja-ic show the respective areas, a, b, and c, enlarged twice. 



This cycadeoidean strobilus occurs preserved as impressions on flat slabs in plant- 

 bearing bed a of the Trias of Bjuf, Southern Sweden; and in accord with William- 

 son's original conception of the disk of Zamites gigas (202) it has been supposed to 

 represent a disk composed of inwardly-deflexed carpellary fronds. But while not pri- 

 marily impossible that such disks should occur, it is more likely that in the present 

 instance fructification is bisporangiate. If so the bodies at c (figure ic) are not 

 megasporangia but synangia, and there must be present beneath them an apical ovulate 

 cone much like the silicified cone seen in longitudinal section in photograph 4. In 

 either case figure I shows a very instructive example of the preservation of strobilar 

 forms like the foregoing silicified strobili as impression. 1 ; on Hat slabs. Each of these 

 two modes of preservation aids in the interpretation of the other. For the meaning 

 of the structures at b and c, see photograph 3 below. 



Photographs 2 and 3. — Cycadeoidea dacofensis. External view of an upper and a 

 lower portion respectively of an ovulate strobilus divested of its enveloping bracts. In 2 the 

 rachis of the staminate fronds of the disk are also split or eroded away in all the upper 

 region, disclosing the synangia at c and the insertion of the pinnules of the sporophylls at 

 p, p. Moreover, the long, deep furrows mark the inner edge of each microsporophyll rachis, 

 and the branches sent from these the inner edges of the alternately inserted pinnules, thus 

 clearly indicating the once-pinnate character of the microsporophylls or staminate fronds 

 into which the staminate disk divides. Note especially that the pairs of pinnule insertions, 

 p. p, are not those of the same, but two adjacent rachides. While this surface is not pre- 

 cisely the same as at points a and ft, figure 1, there is relative similarity, and it seems pretty 

 clear that in both instances the attachment of the pinnules of a once-pinnate frond laterally 

 to the rachis is indicated. 



Photograph 3. — Showing the basal region of the strobilus. The fronds of the disk are 

 not split away and the surface features are precisely comparable to those of Cycadocephalus 

 (figure 1). 



Photograph 4.— Cycadeoidea dacofensis. T. 214. S. 360. X 5- View of central ovulate 

 cone enlarged four times. It will be observed that a thin zone of clear silica lies outside the 

 tips of the small micropylar tubes and the interseminal scales. 



As already noted in the text, this would make possible the development by polishing 

 such a cone so as to display its surface features in great perfection. The obliquely set pedi- 

 cels and scales of the lower right-hand portion of the cone are in part cut nearly trans- 

 versely. On the left the very young seeds are especially well indicated and a number are 

 cut in so exactly the median longitudinal plane that the entire lengths of the micropylar 

 tubes appear. 



Plate XL VI. Williamsonia gigas Carruthers. 



Various imprints and casts of strobili from the Yorkshire coast, now partly in the 

 Paris Museum. From Saporta, Plantes Jurassiques, vol. iv, plates xvm and ccxlvi (125). 

 The interpretation of these fossils as given in the following legends differs from that of 

 Saporta. All figures X 0.8. 



Figure I. — Cast reproduction of specimen shown in figure 4, exhibiting the true out- 

 line of the basal portion of an ovulate strobilus with its surrounding bracts. Receptacle 

 globular; only the closely set basal and sterile sporophylls and scales being indicated. Such 

 a strobilus might or might not have earlier borne an hypogynous staminate disk. The size 

 as well as the general form and appearance of the bracts, the receptacle, and the sterile 

 basal region all find their near counterpart in the silicified strobili borne by several of the 

 Black Hills trunks, notably the fine specimens of Cycadeoidea dacotensis. The Yorkshire 

 fruit on which the reproduction i^ based must in fact be closely related to the silicified C. 

 dacotensis specimens generically if not even specifically. One of the main differences in 

 general appearance is due to the completer preservation of the latter, including the profuse 



