KUNGL. SV. VET. AKADEMIENS HANDUNGAR. BAND 57. N:0 |. 17 



garded as merely varietal, or possibly as tlie normal state of the immature or barren 

 plants». Solms-Laubach (1895, p. 73) speaks of these specimens of var. ornatum as 

 »gut erhaltene Exemplare der Pflanze», and they are further figured by Gilkinet (1875, 

 pl. 39) under the name of Psilophyton princeps. D. White (1905, p. 61), as a result of 

 his examination of a part of Dawson's material, says: »There is, however, I believe, 

 little doubt that the so-called variety ornatum represents the original type species of the 

 genus, its varietal discrimination being of doubtful validity». 



In agreement with the opinions just quoted, I regard the specimens figured by 

 Dawson in 1871 under the name of var. ornatum as typical representatives of Psilophy- 

 ton princeps. These specimens represent indeed the first really characteristic material 

 figured under that name. The diagnose should therefore be based chiefly on these spe- 

 cimens; but as some at least of the branches with leaves. or scars figured in 1859 may be 

 regarded, in accordance with Dawson' s opinion, as specifically identical with this form, 

 it may be possible still to regard the species as dating from 1859, despite the fact that 

 the best preserved material was not figured until 1871. A consequence of this will be 

 that the var. ornatum will disappear, the specimens on which it was founded being re- 

 garded as typical representatives of the species. Though this manner of solving the 

 difficulty may be somewhat informal, I believe it to be the only way in which the name 

 Psilophyton princeps can be upheld, and at the same time made to cover a definite type 

 of plant which it will be possible to identify with some safety in different localities. 



In accordance with the plan here outlined and with similar opinions already ex- 

 pressed by D. White, there should be referred to Psilophyton princeps only stems which 

 show spines or spine-scars and which agree with the specimens figured by Dawson (1871) 

 as Psilophyton princeps var. ornatum or differ from them only in having somewhat smaller 

 and more rudimentary leaves. On the other hand, the following kinds of plant-remains 

 now usually referred to Psilophyton princeps should not be included in this species unless 

 there are special reasons, such as actual connection etc: — (1) specimens without spines 

 or spine-scars but with the internal structure described by Dawson as characteristic of 

 Psilophyton princeps; (2) isolat ed, bifurcating branches (Hostimella-type) without spines 

 or spine-scars, even if characterized by circinate vernation; (3) supposed fructifications 

 figured by Dawson under the name of Psilophyton princeps or specimens agreeing with 

 them (= Dawsonites arcuatus, see below, p. 24). 



The majority of specimens referred by various authors to Psilophyton princeps 

 should therefore be removed from that species. The reduction of the species resulting 

 from this treatment of the material is well illustrated by the short list of records given 

 above, only figured specimens agreeing with the narrower definition being there men- 

 tioned. 



Description of specimens. 



Of the numerous specimens from Röragen which may be referred to Psilophyton 

 princeps those with the spines preserved in connection with the stems should be regarded 

 as the most typical. Specimens of this kind are shown for instance in the photographs 

 in pl. 1, figs. 24 — 31, and in the drawings in pl. 4, figs. 9 — 13. There is another group of 



K. Sv. Vet. Akad. Handl. Band 57. N:o 1. 3 



