346 CABDIOCARPAI/ES [CH. 



their origin below the sclerotesta. In the course of the vascular 

 bundles Mitrospermum is intermediate between Rhabdospermum 

 and Taxospermum. 



This genus is founded on a detached seed, but its resemblance 

 to undoubted Cordaitean species favours its attribution to that 

 group though, as Mrs Arber points out, some markedly platy- 

 spermic seeds are known to have been borne on fern-hke fronds 

 and Mitrospermum may belong to some genus of Pteridosperms, 



Diplotesta. Brongniart. 



Diplotesta Grand' Euryana Brongniart. The generic name 

 Diplotesta, suggested by Grand'Eury, was given by Brongniart^ to 

 a Grand'Croix seed which he compared with that of the Conifer 

 Cephalotaxus. The type-specimen is elhptical and platyspermic 

 (fig. 495, H, p. 322), and differs from Taxospermum in the cordate 

 form of the seed-cavity, also in the more restricted union of nucellus 

 and testa. The testa is difierentiated into a sarcotesta (sa) and 

 sclerotesta, and the latter forms two feebly developed keels in the 

 principal plane : a characteristic feature shared with Mitrospermum 

 is the sphtting of the shell into two equal valves (fig. 495, F). 

 Fig. 495, H, shows the contracted cyUndrical nucellus and the 

 pollen-chamber: the sarcotesta (sa) is only partially preserved. 

 Diplotesta differs from Cardiocarpus in the course of the integu- 

 mental vascular bundles which are of the type illustrated by 

 Rhabdospermum, Taxospermum, and Cyclocarpus, but from these 

 genera it is distinguished by the dehiscence of the shell, also by 

 its form and certain anatomical features as described by Brong- 

 niart and Bertrand^. 



In this genus Bertrand includes Brongniart's species Sarcotaxus 

 avellana (fig. 495, F), a correlation suggested by the latter author. 



Leptocaryon. Brongniart. 



Brongniart* founded this genus for a single species, Leptocaryon 

 avellana, represented by a Grand'Croix specimen 12 x 10 mm., 

 which he beheved to be related to Taxus. Leptocaryon differs 



1 Brongniart (74) p. 247, PI. xxi. figs. 12—14; (81) p. 21, PI. A. fig. 12; PI. xiv; 

 Renault (80=) p. 106, PI. xv. figs. 12, 13; Grand'Eury (77) A. p. 239, PI. xxvi. 

 fig- 27. 2 Bertrand, C. E. (07^). 



^Brongniart (74) p. 248, PL xxi. fig. 17; (81) p. 22, PL A. fig. 17; PL vi. 



