Dr. E. A. Newell Arber — Coal-measure Calamites. 218 



to other types of Calamite pith-casts we have to confess our inability 

 to do so in strict terms. 



There are a certain set of Calamite form -species which have given 

 me much trouble in this respect, but until recently I have not 

 understood why. It is a common observation that such specimens as 

 I refer to here more particularly, never show the prints of the 

 infranodal canals below the nodes. These scars in my experience 

 offer one of the best, if not the most satisfactory, means we have of 

 discriminating between form-specits among pith-casts, considered, of 

 course, in conjunction with other morphological features. I have, 

 however, now realized that these specimens are not, strictly speaking, 

 pith-casts at all. They represent incrustations of surfaces which 

 lay external to the pith, and I propose to distinguish them as 

 submedullary casts. In such cases the tissues appear to have under- 

 gone more or less considerable decay before the cast Avas formed, no 

 doubt to an extent which varied greatly in different cases. The 

 result has been that a cast has been formed of the medullary rays and 

 bundles at a level which lay external to the true pith-cavity and the 

 openings of the infranodal canals into that region. 



I first realized this fact from a study of a slightly tangential 

 section ' of the wood of a petrified stem of a Calamite, passing through 

 a node, in my friend Dr. Scott's collection. Part of this section is 

 figured by Dr. Scott ^ in his Studies in Fossil Botany, so I need 

 only refer to it briefly here. At this level the so-called " infranodal 

 canals " consist of solid masses of tissue, which would leave no print, 

 on the cast. It is only the somewhat expanded terminations of the 

 canals pi;ojecting into the pith-cavity which gives rise to the well- 

 known scars. 



This section of Dr. Scott's appears to me to throw a flood of 

 light on such frequently quoted and figured species as Calamites 

 cannceformis, Schlotheim, 1820; C. pachy derma, Brougn., 1828; 

 C. approxitnatus, Brongn., 1828 {non Schlotheim) ; C. varians, Stern- 

 berg, 1838; C. Schiitzei, Stur, 1881; and C. ScJiatzlarensis, Stur, 

 1887. 



These specimens are often characterized by the coarseness of the 

 ribbing of the internodes. There are, for instance, in the Sedgwick 

 Museum, Cambridge,^ several examples of large Calamite casts 

 from the Dogtooth Rake Ironstone, Chesterfield, with ribs 5-6 mm. 

 broad, without any trace of infranodal canals. These appear to 

 correspond very closely to the C. paehyderma of Brongniart, and they 

 are clearly submedullary in origin. C. ScJiatzlarensis of Stur 

 appears to be a name founded on several different types of pith- cast, 

 and the same is true of that author's C. Schiitzei. 



C. varians, Sternb., is also indefinable, and nothing is gained 

 bj' transferring C. approximatus, Brongn. {non Schlotheim) to Stur's 

 species C. Waldenlurgensis (as has recently been suggested by Kidston) 

 or to an entirely new species, C. Schiltzeiformis, forma Waldetiburyensis, 



^ No. 897. 



2 2nd ed. (1908), p. 27, fig. 8 ; see also pp. 47-8. 



' Nos. 439-41, 478. 



