503 
Mitrospermum compression ( Will.). 
two branches before entering the shell. These two branches remain outside 
the shell throughout their entire course. He contrasts this type of vascular 
system with that of Rhabdocarpusl in which the main supply bundle passes 
unbranched through the shell. The two lateral bundles arise from the 
chalazal vascular plate, and immediately run down again through the shell, 
forming an acute angle with the main bundle. Bertrand names them 
‘ faisceaux recurrents ’. On emerging from the shell, they curve upwards 
and follow the same course as the bundles of Cardiocarpus. Brongniart’s 
Cardiocarpus nummularis and C. tenuis have the rhabdocarpic type of 
vascular symmetry, and hence are removed from Cardiocarpus and placed 
in Cyclocarpus. 2 
In Mitrospermum compressum the vascular system 3 is intermediate 
between that characteristic of Rhabdocarpus and of Taxospermum . 4 In the 
latter the branch bundles, as in Rhabdocarpus , arise from the chalazal 
vascular mass, but they follow the floor of the shell cavity, and on reaching 
the flanks traverse the shell obliquely from below upwards. 
Since the seed described in this paper cannot strictly be referred to 
Cardiocarpus (in Bertrand’s sense), or to any of the related genera, it seems 
advisable to distinguish it by a new generic name. I suggest that Mitro¬ 
spermum might be used in allusion to the form of the seed-base. 
Mitrospermum , gen. nov. 
The characters of the genus are at present those of the only known 
species:— 
Mitrospermum compressum (Will.). 
1877. Cardiocarpo 7 i compressum , Will. W. C. Williamson, On the 
Orga 7 iization of the Fossil Plants of the Coal Measures , Pt. VIII, p. 279. 
Bilaterally symmetrical seed, flattened in the plane of symmetry. 
As usually preserved, the integument consists of a sclerotesta of thick-walled 
cells, enclosed in a more delicate sarcotesta, which extends into a wing in 
the principal plane. An outer layer of large mucilage cells is the most 
conspicuous feature of the sarcotesta. In the best preserved specimens, in 
addition to the parts of the integument just described, two other layers can 
be recognized, namely, a thin-walled tissue lining the sclerotesta, and a 
small-celled layer clothing the mucilage cells of the sarcotesta. The main 
vascular bundle enters the hilum, and passes through the sclerotesta without 
branching. Below the base of the nucellus, it gives off two strands in the 
principal plane, which are at first horizontal, but soon dip slightly down¬ 
wards and outwards, traversing the sclerotesta in an oblique direction. 
1 Bertrand (’07 4 ). 2 Bertrand (’08 2 ). 8 See p. 497. 
4 Bertrand (’07 1 ). 
