FLOKA OF THE KUOTAMK FOUMAIJUN. 299 



li!u\ wliicli is. howTvoi-, shai'ply dofiiu'd. In this way a portion of the 

 .stem lieiioath each node is strongly striate, the striated portions being 

 formed In- the united tecMh. which produce a sheath. This latter is 

 pressed close to the stem and apparently coalesces with it. The cross 

 section of the furrows on the sheath is N'-sliaped, and when casts of them 

 ai'c taken in llie fine shale, as is conuuonly the case, they appear as .sharp- 

 toppcnl ridges, widening toward the nodes. In this form the\- simulate 

 teeth. The teeth are rarely found preservcnl, hut connnonly break off 

 at the nodes, where they coalesce with the stem and leave more or less 

 distinct truncate processes, which coi'respond with the basics of the 

 teeth. The most common foi'm pre.s(>i'ved by the remains of this Equi- 

 setum is a strap-shaped poition of the stem, composed m.-iinly of 

 epidermal tissues, which shows a varying numbei' of nodes with sti'onglv 

 striate portions beneath each node. Each node cai-i-ies mostly I'ather 

 vague, squai-e-topped processes. Tn \-ery rare cases a few teeth are 

 pi-eserved. Judging fi-om ihv stria- and processes, the number of teeth 

 seems to have been about 'M), for as many as 13 processes have been 

 counted on the upper face of some of the stem imprints. In a few cases 

 the stem, at a node, has been compressed in the direction of its a.xis, so 

 that the mud has been squeezed up through the node, carrying tlie dia- 

 phragm away, and in one or two cases it may l^e seen in place. In this 

 way we may account for the frequent occin-rence of isolated diaphragms. 

 Diaphragms of varying size, occurring detached from the stems, are 

 not uncommon on some pieces of the shale. They vary from 5 nun. or 

 less to about 1 cm. in diameter. They occur anywhere, sometimes on 

 some portion of the macerated remains of the stem and sometimes on the 

 shale, without any trace of the stem. They are wheel-shaped, with a 

 round hole in the center, around which radiate club-shaped convexities 

 that have their thicker portions at the periphery of the circle. When 

 the nodes are compressed in an axial direction and some of the teeth are 

 preserved they sometimes appear unusually long, since the sheath splits 

 some distance down along the sinuses and thus separates the basal portions 

 of the teeth that were formerly consolidated to form the sheath. At 

 least that is the way I account for the unusual length of the teeth in the 

 sheath compressed in an axial direction, which is shown in PL LXXII, 

 Fig. 7. 



