64 PTERIDOSPERMEAE [CH, 



of the sporangial wall Mittagia also resembles the sporocarp of 

 Pilularia. 



Seeds presented as impressions, without internal structure, 

 superficially resembling Lagenostoma. 



Lagenospermum Nathorst. 



This generic name is adopted for seeds represented by casts 

 or impressions agreeing in external features with Lagenostoma 

 but which on the available evidence cannot be confidently 

 assigned to that genus 1 . Two types of seed were described by 

 Arber 2 from the Lower Coal Measures of Scotland as Lagenostoma 

 Kidstoni and L. Sinclairi: the former has been removed by 

 Oliver 3 to PTiysostoma and both are included by Arber 4 in a 

 recent paper in the genus Radiospermum. This new generic term 

 is proposed by Arber for a number of small sub-cylindrical seeds 

 founded on impressions including 'small seeds which, when the 

 structure is preserved, are known as Lagenostoma, PTiysostoma^ 

 and Conostoma.' The question of nomenclature is invariably 

 raised by cases in which impressions resemble in their superficial 

 characters genera founded on anatomical characters : the seeds 

 originally referred to Lagenostoma Sinclairi afford a good example 

 of this difficulty. Nathorst has recently proposed the generic 

 name Lagenospermum as preferable to Lagenostoma and Radio- 

 spermum in the case of Lagenostoma Sinclairi and similar seed& 

 which afford no proof of the possession of such morphological 

 characters as would justify their inclusion in the genus Lagenostoma 

 but which may be examples of that genus. As Nathorst points 

 out, the adoption of Radiospermum for L. Sinclairi is inadvisable 

 on the ground that it is also applied to seeds of a different type. 

 The type-species of Lagenospermum is L. Sinclairi and Nathorst 

 describes additional species from Lower Carboniferous rocks in 

 Spitzbergen. 



Lagenospermum Sinclairi (Arber ex Kidston MS.). 



Although it is not certain that these seeds are morphologically 

 identical with the genus Lagenostoma, a brief description is inter- 



1 Nathorst (14) p. 29. 2 Arber (05). 



3 Oliver (09). 4 Arber (14) p. 102. 



