N0.1U1. FOSSIL CYCADS FROM THE BLACK HILLS— WARD. 207 



their natural position can not of course be demonstrated, but the other 

 specimens do not negative this view. 



Piofessor McBride remarks that "the present species is near Be7i- 

 nettites gibsonianus Carr., from which it may be distinguished by 

 greater size and by the fact that in our species the libro-vascuhir bun- 

 dles of the leaf-stems are of uniform size and distribution, and do not 

 form a horseshoe shape in cross section, as is said to be the case in the 

 English species." In this last one would su])pose he was confounding 

 the undivided vascular bundle as it appears in the axis, and esi)ecially 

 in its passage through the cortical layer' before it divides, with the 

 form assumed by the numerous strands that enter the petiole and 

 ai)pear as small dots on a cross section of the latter.- Neither in the 

 American Geologist nor in the Bulletin of the Laboratory of the State 

 University of Iowa do these strands show clearly in fig. li, still I think 

 I can detect them, but in nearly all our specimens these bundles are 

 very clearly shown, and they do agree remarkably well with those of 

 Carruthers's figure.^ Still I should hesitate to refer the American forms 

 to C. (jibsoni on this character alone, and having myself examined the 

 British sj)ecimen I do not think it is very close in other respects.' 



The absence of perfect trunks of this species in the U. S. National 

 Museum collection is not due to its rarity in the Black Ilills, as I was 

 satisfied after exy^mining the large number of fragments picked up 

 by myself, but to the frailty of the siiecies. There is in fossil cycads 

 certainly a close connection between the mineral constitution and the 

 original nature of the tissues, and both vary with the species, much as 

 different kinds of wood differ in their qualities of hardness, durability, 

 tenacity, etc., in our living forests. Accordingly the substance of the 

 rock in this species is always soft, porous, and light, easily worn by 

 attrition, and therefore frail. Moreover there is a tendency to early 

 decay of the medulla and woody axis, which caused many of the trunks 

 to become hollow before they were entombed. This made compression 

 and general destruction easy and accounts for the difdculty in securing 

 good specimens. 



In view of these facts I was not surprised to find a large number of 

 specimens of this species in the Yale collection. There are no less than 

 13 which I have so referred, although several of these are very abnor- 

 mal and doubtful. The ones so classed are Kos. 8, 10, 23, 26, 27, 29, 38, 

 42, 4G, 53, 73, 76, and 110. No one of these is absolutely complete, 

 and the greater part of them are mere fragments. In the majority of 

 cases the specific determination is clear at a glance, and this is true 

 even of the smaller fragments. No. 10 is a typical and nearly comi)lete 

 trunk, weighing 51.46 kg., and No. 23 is by far the most i)erfect speci- 

 men of the species known to me. It weighs nearly 50 kg., but there is 

 a vast cavity at the summit. No. 76 is also nearly complete and a fine 



' Carruthers, Trans. Liun. Soc, XXVI, ])1. lvii, fig. 3. 



^Idem., 1)1. LViii, lig. 2. 



=» Sixteenth Ann. Kept. U. S. (kol. .Sixrv., I't. 1, p. 187. 



