OF THE BRITISH COAL MEASURES. 99 
investigated by Count Solms-Laubach *, the first division takes place further 
out. These plants thus present interesting analogies with the polydesmie 
species of Heterangium, though never, of course, any exact agreement. I 
think this is really the most fertile comparison we can make, and that the 
polydesmic petioles of our Coal-Measure Heterangiums may well be described 
as showing an approach to the Aalymma (Calamopitys) structuref. Even 
here there can be no question of filiation. The species of Calamopitys are 
probably older than any known ZZeterangium, and certainly much older than 
any which have been found to have polydesmic petioles. 
While, then, Heterangium is directly connected with Lyginopteris through 
the intermediate species discovered by Dr. Kubart, we have no evidence that 
the polydesmie forms indicate a transition to any other genus. They present 
interesting analogies with the Medulloseze and Calamopityez, and show that 
there was more in common between these groups and the Lyginopteride» 
than has hitherto been supposed. But we have no sufficient grounds for 
assuming any direct evolutionary connection. 
; SUMMARY. 
The characters of the various species described have been given above 
(pp. 65, 73, 89, 91). The more general results may be summed up as 
follows :— 
l. The three British Coal-Measure species, Heterangium shorense, H. 
tilieoides, and H. Lomavii, agree in their more important characters and 
only differ in details. The fourth species, /7. minimum, is of a different type. 
2. The three species first named may conveniently be grouped in a pro- 
visional subgenus, Polyangium, characterized by the leaf-trace, starting from 
the stele as two distinct bundles, which further divide on their outward 
course, the number of bundles in the petiole ranging from four to eight. 
9. In addition to the polydesmie structure, these three species further agree 
in the sharp delimitation of the primary peripheral xylem-strands, with the 
consequent differentiation of large interfascicular principal rays, and in the 
approach to exarchy in the peripheral strands and leaí-trace bundles, the 
primary centrifugal xylem being comparatively little developed. 
4. It is probable that, besides H. shorense, H. tilieoides, and H. Lomaazii, 
the four species described by Renault, from the Upper Coal Measures of 
* Solms-Laubach, 1896, p. 67. 
+ There is no reason to believe that the protostelic structure of the stem existed in 
Calamopitys Saturni, Unger, or in the two species (C. fascicularis, Scott, and C. Beinertiana 
(Goeppert)) separated by Dr. Zalessky, under the name Eristophyton (Zalessky, 1911, p. 27). 
I am not sure that I agree with Dr. Zalessky in his proposed division of the genus, 
C. Saturni seems to have in some respects more in common with my C. fascicularis than with 
C. annularis or C. americana. The whole question is discussed in a forthcoming paper on 
the genus. 
eee ee Pt 
