334 CAEDIOCABPALBS [CH. 



a view to avoid the risks necessarily entailed by following this 

 practice it is suggested that a clearer distinction should be drawn 

 between genera based primarily on structural features and form- 

 genera. The following notes on the genera Cardiocarpus, Cordai- 

 carpus, Cyclocarpon, Cycadinocarpus, Jordania, and Samaropsis, 

 may serve to illustrate some of the difficulties connected with the 

 terminology of Palaeozoic seeds. 



Cardiocarpus. Brongniart^ proposed the name Cardiocarpon 

 in 1828 for Upper Carboniferous seeds described as compressed, 

 lenticular, cordiform or reniform 'fruits' with an acute apex: 

 in his later work^ he recognised their true morphological nature 

 and gave an account of some exceptionally well-preserved examples 

 from Grand' Croix. Brongniart in common with other authors 

 beheved Cardiocarpus seeds to belong to Cordaitean plants, a 

 view that in several cases is based on conclusive evidence. The 

 specimen represented in fig. 501, D, illustrates the characteristic 

 form of a cast of a Cardiocarpus seed, and the sections shown in 

 fig. 501, A and B, are from an identical or a very closely alUed 

 species. The generic characters are : (i) the presence of a narrow 

 flattened border or wing surrounding a platyspermic nucule, 

 (ii) the cordiform base and more or less pointed apex, (iii) the 

 differentiation of the testa into a sarcotesta and sclerotesta free 

 from the nucellus except at the base, (iv) the 'tent-pole' prolonga- 

 tion of the prothallus (fig. 510, A, h) and the presence of a fairly 

 large pollen-chamber, pc, (v) the occurrence of two sets of .vascular 

 bundles, an inner nucellar series and two double vascular strands 

 (fig. 500, A, V, B) which are given off from the main supply before 

 it reaches the sclerotesta. The term Cardiocarpus as used by 

 Brongniart signifies a type of seed possessing both certain ana- 

 tomical and external characters. The proposal is to restrict the 

 generic appellation to seeds exhibiting definite structural features 

 agreeing in essentials with Cardiocarpus sclerotesta and C. drupficeus. 



Cordaicarpus. This name was first employed by Geinitz* in 

 the form Cordaicarpon, the type-species being C. Cordai (fig. 502, 

 C) from the Coal Measures of Germany, a seed referred by the 



1 Brongniart (28) A. p. 87. ' Brongniart (74) p. 245 (81). 



» Geinitz (62) p. 150; Kidaton (11) p. 240; Geinitz (55) A. PI. xxi. figs. 7—16. 



