EXTERNAL MORPHOLOGY OF THE STEMS OF CALAMITES. 513 
aware their distribution is the same in both cases. In size and shape the 
individual scars vary not only in different species of Calamophloios but in 
different specimens of the same species. As a rule, where the branch scars 
are approximated they are not all of exactly the same size. They appear to 
be typically quadrate in form with a central umbilicus. Where the scars 
in a whorl are crowded the form is sometimes more or less oval or circular. 
Among British specimens there are, so far as we are aware, no great differ- 
ences as regards the shape of the branch scars, as there are, for instance, 
among certain foreign species, especially C. semicircularis, Weiss. 
In many examples the limits of the branch scars are ill-defined or the 
details are obscure (cf. Pl. 25. fig. 24). 
Root sears.—The prints of root scars vary in size and are indefinite in 
shape. They are found both at the nodes and also in some cases scattered 
over the internodes (P1. 28. fig. 8, Pl. 24. figs. 15, 20, Pl. 25. fig. 21). 
3. The Correlation of Specimens exhibiting the external features of 
certain stems with their pith casts. 
We now come to consider the possibilities of correlating specimens show- 
ing the true external features of the stems of Calamites with the pith casts. 
Although so little attention has been devoted to the former type of 
incrustation, we know already that this question presents more difficulties 
than might at first sight be imagined. It is especially in view of these facts 
that it has been regarded as necessary to erect the genus Calamophloios. 
It is only quite rarely that the same specimen shows both the external 
surface of the stem and the pith cast. This is the case in the specimen of 
C. undulatus (Pl. 94. fig. 15), the reverse side of which shows the pith cast, 
and in the two examples of C. Suckowi (figs. 11, 12) figured here. 
As a rule, only one type of preservation is seen in a particular specimen. 
Supposing that type to be the external surface, can one be certain it always 
belonged to one particular type of pith cast, or vice versa? We think there 
is already evidence to show that this is not a safe assumption, and that the 
external surfaces of these stems frequently present stereotyped morphological 
features. 
Dr. Jongmans * has stated that when studying C. paleaceus, Stur, he bad 
become convinced that this species must represent the external features of 
C. ramosus. It was only when Dr. Kidston pointed out to him that this 
could not be the case, since the foliage and fructifications of these two 
Calamites are quite unlike, that he realised that the external surfaces of 
C. paleaceus aud C. ramosus are practically indistinguishable. 
Thus the name Calamophloios rugosus Arber, is here used as a type of 
* Jongmans (1911) p. 122, 
