OF THE BRITISH COAL MEASURES. 75 
Heterangium which it is proposed to keep distinct is the little stem described 
in a subsequent section of the paper under the name /7. minimum (p. 90). 
The reasons for the conclusions arrived at will appear in the course of the 
description. I take the 8 form first, because the best specimens belong to 
it, and it has never been properly described. Its relation to the æ form is 
not very obvious, though I think Williamson was right in uniting them. 
H. Lomazii, Form £. 
The specimens of this form are associated with those of the « form and of 
** H. eylindricum." All appear to have come originally from the same block. 
I have enumerated in the footnote * seven specimens of the 8 form, though 
more than one may possibly belong to the same stem, as in the case of 5 and 6. 
The preservation of the outer tissues is seldom so complete as to render 
any very accurate measurements of the stem practicable. Roughly speaking, 
the dimensions of the different specimens range from 17x10 mm. to 
7x4 mm., or, allowing for compression and distortion, the diameter may be 
said to vary from about 13 mm. to about 5 or 6 mm. 
The general form of the stem, to judge from the least-distorted specimens, 
seems to have been nearly cylindrical. The leaves appear to have been, as a 
rule, borne on the stem at long intervals, for many of the sections show 
the trace of only one leaf, and unfortunately no section happens to pass 
through an evident leaf-base in connection with the stem. The best-preserved 
specimen is No. 5 (Pl. 2. Phot. 13) ; from the considerable development of the 
phloem, this stem at first sight recalls H. tilivoides, but from its structure 
must be referred to H. Lomawii. 
The Stele. 
The more or less compressed primary wood varies in the different specimens 
from 8 x 2 mm. to 3 x 1 mm.—say, from 4 or 5 mm. to about 2 mm. in diameter 
if restored to its presumably cylindrical natural form. Its size is by no 
means always proportional to that of the stem, owing to large differences 
in the development of the secondary tissues. 
The arrangement of the metaxylem tracheides is not very regular (PI. 2. 
Phots. 9, 12), the groups being less definite in form and size than those of 
* For reference letters see above, p. 67. 
Specimen 1.—7 transverse sections : W. 1915, 1915 A, 1915 B, 1915 C; Q. 6, Q. 11; S. 447. 
Specimen 2.—8 transverse sections: W., 1915 H ; Q. 64; S. 445. 
Specimen 3.—' transverse sections: W. 1304 A, 1915 P; R. 621; S. 444, 446 ; N. 7, 19. 
The longitudinal sections W. 1915 G and 1915 R probably belong to this specimen; possibly 
R. 638 also. 
Specimen 4.—9 transverse sections: W. 1915 R; R. 645. 
Specimen 5.—2 trausverse sections: R. 639; S. 625. 
Specimen 6.—3 transverse sections : W. 1915 D, 1915 E, and probably N. 3. 
Specimen 1.—9 incomplete transverse sections : IBI0b7; N, 8. 
Where necessary, the order of the sections in a series is given in the text. 
G2 
