FOSSIL CYCADEAN TRUNKS FROM WYOMING 269 



which, for some reason, there is no outer layer, to the left of which it 

 extends entirely to the margin, and on the right of which it fills a deep 

 depression in the surface. PI. XIX includes the greater part of the por- 

 tion on the left where this layer is present, and PI. XX covers the area 

 on the right. All the characters, generic and specific, are admirably 

 brought out in these two enlarged areas, especially the nature of the 

 ramentum outside of the armor, and its wavy, crinkled character as 

 determined by the irregularities of the surface and the unknown agen- 

 cies that compressed it from without and packed in down against the 

 trunk. In several places portions of leaf bases and perhaps of repro- 

 ductive organs, detached from the armor and caught, as it were, in the 

 meshes of chaff, can be seen lodged in the outer coat. These show 

 their normal vascular structure under the compound microscope. 

 Owing to inequalities of pressure and unexplained conditions the long 

 strands of matted chaff are differentiated into bands of different color 

 and density that lie parallel to one another and zigzag across the ex- 

 posed cross-sections of the investing layer. Near the left margin of 

 PL XX there is a region where one of the petioles is clearly seen to 

 cross the boundary line between the armor and the ramentaceous cov- 

 ering, and the chaff that developed from its left side can also be traced 

 across this boundary and out into the outer layer. This is particularly 

 instructive from the point of view of the origin of the latter. Upon 

 the whole these several illustrations afford a tolerably clear idea of the 

 character of this remarkable group of extinct plants. 



CYCADELLA COMPRESSA n. sp. 



Trunks small (io-20cm high, with major diameter 12-15001), or- 

 iginally conical, all much compressed laterally or sometimes vertically 

 or obliquely, unbranched ; rock soft, light colored, of low specific 

 gravity ; organs of the armor tightly appressed to the trunk for the 

 most part upwardly, obscuring their arrangement ; leaf scars subrhom- 

 bic, where normal i5-2omm wide and 8— 12mm high ; leaf bases soft, 

 rough or porous; walls i-2rnm thick, soft sandy or decayed and de- 

 pressed, light colored or yellowish ; reproductive organs few and ob- 

 scure, sometimes slightly elevated, elliptical in cross-section, 12 X 20mm 

 in diameter, with or without visible bract scars, the central portion 

 obscure; armor very variable in thickness (5-25mm), joined to the 

 axis by a definite but more or less irregular line ; wood 2cm thick ; 

 cortical parenchyma icm thick; fibrous zone icm thick, not differ- 

 entiated; medulla in laterally compressed specimens a thin slab 5mm 

 Proc. Wash. Acad. Sci., Februarj-, 1900. 



