2 PROF. MARGARET J. BENSON ON 



divergence from the type under consideration than was formerly suspected — in fact, 

 as the authors of the above treatise suggest, the resemblances of Sphserostoma with 

 Lagenostoma are greater than with Conostoma* Hence one has been obliged to found 

 a new form-genus for the geologically older type, and the term Sphserostoma was 

 chosen because of the rounded form of the free part of the nucellus within which lies 

 the pollen chamber. Before proceeding to describe the ovule, I wish to express my 

 indebtedness to Professor I. Bayley Balfour, who presented me with the large block 

 of Burntisland rock from which all but two of the slides used in the present paper have 

 been obtained. 



One of these is a slide most generously put at my disposal by Dr D. H. Scott, 

 F.R.S. In the course of the paper it will be shown how much is derived from this 

 slide which, as a section of a Pettycur petrifaction, cannot, I think, be surpassed for 

 beauty of workmanship and interest of content. I take this opportunity of expressing 

 my gratitude to Dr Scott for this loan. The other slide is a fine radial section of 

 the ovule, cut by Dr Gordon, a photograph of which Dr Gordon has been kind 

 enough to send me (vide PI. II. fig. 8). 



Sphserostoma ovale has so far only been recorded from Pettycur deposits of the 

 Calciferous Sandstone series of Scotland. In these it occurs at rare intervals, but 

 generally, when found, is fairly abundant. About fifty have been sectioned from 

 the above-mentioned block, but owing to the impossibility of orienting such small 

 objects, a large proportion are cut obliquely. They are always closely associated with 

 the vegetative organs of Heterangium Grievii, and hence the ovule has long been 

 suspected of being the megasporangial apparatus of this most fern-like of all would-be 

 Pteridosperms. 



Deferring the evidence which I consider places this surmise upon a surer basis, it 

 will be best to describe the ovule in detail. 



II. General Features of the Organisation of the Ovule. 



(Text-figs. 1 and 2.) 



In its complete state the ovule consists of two parts — a central body representing 

 l be nucellus and inner integument, and an enveloping cupule or outer integument. 



For convenience, the inner part will often be referred to as the ovule, for it is most 

 common to find it bereft of its cupule. A reference to text-fig. 1, which represents a 

 restoration of a median longitudinal section of both parts, will readily show their 

 relationship to one another, especially if this restoration be compared with that in 

 text-fig. 2, c. 



Without the cupule the ovule is 3 '5 mm. in length and about 2*2 mm. at its widest 

 part. At first sight its most striking feature is the series of crests forming the so- 

 called "frill" around the micropyle (text-fig. 1,/.). 



* Oliver and Salisbury, loc. cit., p. 38. 



