326 TEIGONOCARPALES [CH. 



whose distinctive characters are derived from their internal 

 organisation, unless there is conclusive evidence to show their 

 identity.' On this specimen Arber 1 has founded a new genus 

 Megalospermum, but as the type-specimen shows no distinctive 

 features other than large dimensions it would seem preferable 

 to retain the more general designation Carpolithus 2 . 



Another example of a seed that may be generically identical 

 with Pachytesta is that described by Lesquereux from North 

 American Coal. Measures as Rhabdocarpus Mansfieldi and more 

 recently recorded by White from Missouri as Rhabdocarpus (Pachy- 

 testa) Mansfieldi 3 . There is little doubt that this and other species 

 of seeds preserved as impressions are examples of Pachytesta but, 

 as Kidston says, it is preferable to reserve the name for specimens 

 showing anatomical features. 



Stephanospermum. Brongniart. 



The genus Stephanospermum, founded by Brongniart 4 on 

 petrified specimens from French Stephanian beds, affords a good 

 example of a radiospermic seed without ribs differing in certain 

 well-marked characters from such seeds as Lagenostoma, Physo- 

 stoma, and Conostoma, notably in the complete separation of the 

 nucellus from the integument and in the possession of a nucellar 

 vascular system. The descriptions by Brongniart and Kenault 5 

 have been extended by the thorough investigations of Oliver 6 . 



Stephanospermum akenioides Brongniart. 



This species is represented by ellipsoidal seeds, 10 mm. long with 

 a maximum breadth of 4 4-5 mm., circular in transverse section. 

 The integument consists of a thick sclerotesta lined internally by a 

 thinner soft layer, the endotesta (fig. 494, A, sc, e), and in all proba- 

 bility covered by an outer flesh or sarcotesta as in Trigonocarpus , 

 though this tissue is not preserved and is omitted from the section 

 shown in fig. 494, A. The sclerotesta is composed of a broad outer 

 band of fchick-walled palisade cells the contracted contents of 

 which are a striking feature in the silicified seeds (fig. 493, F) ; these 



1 Arber, E. A. N. (14) p. 91, PI. vn. fig. 28. 2 See page 364. 



8 White (99) B. p. 267; Lesquereux (79) A. PL 85, fig. 21. 

 4 Brongniart (74) p. 259, PL xxm. figs. 1215; (81) p. 29, PL xvi. 

 6 Renault (80 2 ). 6 Oliver (04) B. 



