326 TBIGONOCARPALES [CH. 



whose distinctive characters are derived from their internal 

 organisation, unless there is conclusive evidence to show their 

 identity.' On this specimen Arher^ 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^. 



Another example of a seed that may be generically identical 

 with Pachytesta is that described by Lesquereux from North 

 American Coal Measures as Rhabdocarpits Mansfieldi and more 

 recently recorded by White from Missouri as Rhahdocarjms {Pachy- 

 testa) Mansfieldi^ There is httle doubt that this and other species 

 of seeds preserved as impressions are examples of Pachytesta but, 

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

 showing anatomical features. 



Stephanospermum. Brongniart. 



The genus Stephanospermum, founded by Brongniart* 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 LagenostomM, 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 Renault* 

 have been extended by the thorough investigations of Ohver® 



Stephanospermum ahenioides Brongniart. 



This species is represented by elhpsoidal 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- 

 bihty 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 thick-walled pahsade cells — ^the contracted contents of 

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



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



" White (99) B. p. 267; Leaquereux (79) A. PI. 85, fig. 21. 

 * Brongniart (74) p. 259, PI. xxm. figs. 12—15; (81) p. 29, PI. xvi. 

 s Renault (&W). 6 oUver (04) B. 



