X] CALAMITINA. 367 



cast of such a stem would show undulating ridges and grooves 

 on one side and straight ones on the others 



A convenient classification of Calamite casts was proposed 

 by Weiss in 1884, founded chiefly on the number and manner 

 of occurrence of branch-scars — or rather branch-depressions — 

 on the surface of pith-casts. Weiss ^ recognised the imper- 

 fection of his proposed grouping, and Zeiller^ has also expressed 

 reasonable doubts as to the scientific value of such group- 

 characters. Weiss instituted three subgenera — Calamitina, 

 Eucalamites and Stylocalamites, which are made use of as 

 convenient terms in descriptive treatment of Calaraite casts. 

 The following account of a few of the more typical casts may 

 serve to illustrate the methods employed in the description of 

 such specimens; the synonomy given for the different species 

 is not intended to be complete, but it is added with a view to 

 drawing attention to the necessity for careful comparison in 

 systematic work. 



A. Calamitina. 



This sub-genus of Calamites, as instituted by Weiss ^, 

 includes Calamitean stems or branches, which are characterised 

 by the periodic occurrence of branch-whorls usually represented 

 by fairly large oval or circular scars just above a nodal line 

 (figs. 99, 100 and 101). The branch-scars may form a row of 

 contiguous discs, or a whorl may consist of a smaller number 

 of branches which are not in contact basally. A form described 

 by Weiss as C. pauciramis, Weiss ^ has only one branch in each 

 whorl, as represented by a single large oval scar on some of the 

 nodes of the cast. A stem of this form is by no means a typical 

 . Calamitina, but it serves to show the existence of forms con- 

 necting Weiss' sub-genera Calamitina and Eucalamites. The 

 number of internodes and nodes between the branch whorls 

 varies in different specimens, and is indeed not constant 

 in the same plant. Each nodal line bears numerous elliptical 

 scars which mark the points of attachment of leaves; each 



1 Seward (88). ^ Weiss (8i), p. 54. ^ Zeiller (88), p. 329. 



» Weiss (76), p. 117; (84), p. 55. " Weiss (84), p. 93, PI. xi. fig. 1. 



