Notices of Memoirs—Heterangiums vm Coal-measures. 128 
the inner layer is thick and granulated, the internal cast is covered 
with corresponding small puncte. Barrande’ was much puzzled 
with these different appearances of the cheeks and ‘glabella, and did 
not offer any satisfactory explanation of them. 
3. In the third group intv which I have arranged the species 
according to their genal characters, the adults have no ocular ridges 
and no ocular tubercles, and the reticulating nervures seem also to 
have disappeared, the shell being smooth and the interlaminar surfaces 
showing no meshwork, though puncte or minute granulations may be 
present. But in some of the largest specimens of 7. concentricus 
from the Oany River there are faint relics of the meshwork. The 
internal casts as well as the external surface of the shell only show 
minute pits or granules as a rule. In the young of TZ. concentricus 
the ocular ridge and ocellus of the species of Group 2 are present, 
according to Beecher, so that their loss seems to be a secondary 
modification or a suppression of larval characters; for the strati- 
graphically later group of 7. se¢icornis possesses them. 
(To be concluded in our next Nwmber.) 
NOTICHS OF MEMOTRS. 
{.—Tse Hererancioms or tae British CoaL-mEasurES. By 
Dr. D. H. Scorr, For.Sec.R.S. 
JILLIAMSON, in his published papers, only recognized two 
British species of Heterangium, Grievii and H. tiliwoides. 
Under the former name he included not only the Lower Carboniferous 
plant from Burntisland, on which the species was founded, but also 
certain Coal-measure forms from Dulesgate. In the joint work by 
Willamson and the present author the same nomenclature was 
adopted, but a second form from Dulesgate was also described under 
the provisional name H. cylindricum. 
HT, tiliwoides, a Coal-measure species from Halifax, remarkable for 
the great development and perfect preservation of the phloem, has 
been kept distinct ever since its first discovery in 1886. 
The enormous difference of age between the Burntisland and the 
Dulesgate plants rendered their specific identity highly improbable, 
and the latter has been separated under the name H. Lomazxii, 
originally suggested by Williamson himself, after the name of the 
discoverer, though not published. H. Lomaxii is characterized by 
the great distinctness of the primary xylem-strands, by their nearly 
exarch structure, with little primary centrifugal wood, by the 
abundant secretory sacs of the stele, and by the rather scattered 
leaves. 
In the Dulesgate material several forms of Heterangium stem have 
been found in association; it is unlikely that they are specifically 
distinct—they more probably represent axes of different orders. The 
provisional species H. cylindricum differs in no important respect from 
LH, Lomaxit, to which it should be reduced. 
1 Barrande, Syst. Silur. Bohéme, vol. i, Trilob., p. 622; ibid., Suppl., 
p. 47. 
