FOSSIL CYCADEAN TRUNKS FROM WYOMING 263 



out beyond the surface and roll over the spaces formerly occu- 

 pied by the leaves and fruits. It seems necessary to assume that 

 this occurred long after the fall of the leaves, and, indeed, this 

 latter doubtless took place much as it does in living cycads, the 

 leaves always forming a crown to the trunk and falling away 

 as the trunk elongates, leaving only their persistent bases to 

 form a false bark. These are not wholly dead, but manifest 

 vegetative activity and doubtless have some physiological func- 

 tion. The development of copious ramentaceous hairs would 

 form a protection to the trunk both from cold and from violence. 



Something analogous to this may be seen in living cycads 

 and in tree-ferns, also in some palms, and a similar function is 

 sometimes performed in other ways, as by the coat of wax on 

 the wax palms. At any rate we are confronted with the fact 

 that Cycadella developed an exuberant growth of fine scales or 

 hairs from the bases of its old petioles below the apex, which 

 formed a woolly or mossy covering of considerable thickness, 

 sufficient when tightly appressed to the trunk and petrified 

 there to form a layer 5-15 mm thick all over the fossil trunks. 



As already remarked, there is usually a clean line of separa- 

 tion between the armor proper and this outer covering, but if 

 the latter consists of ramentum there must be points at which it 

 crossed this boundary and reappeared in the superficial layer. 

 Such points are not easy to find in the collection, but the frac- 

 tured surfaces of a few specimens reveal the process of transition 

 in a more or less imperfect way. Such specimens were carefully 

 searched out and the most promising cases were sectioned and the 

 surfaces polished. Slides were also made and the whole process 

 is as fully illustrated as the nature of the material will permit. 



SYSTEMATIC DESCRIPTION OF THE GENUS AND SPECIES. 



The following is the description of the new genus Cycadella 

 and the species distinguished in the collections examined : 



Genus CYCADELLA new genus. 



PI. XIV. 



Trunks relatively small, bulbous, subspheroidal, or subconical, 

 variously compressed, encased in a layer 5-1 5mm thick of dense lis- 



