24 GESTKGOALES 



[CH. 



Ginhgoites sihirica Heer. 



The specific name sihirica was given by Heeri to one of the 

 most abundant forms in the rich plant-beds at Ust Balei near 

 Irkutsk in Siberia ; the specimens figured from Siberia as Ginkgo 

 sihirica (fig. 635, E), G. Schnidtiana, and G. lepida cannot be 

 regarded as well-defined species ; they agree in the deep division 

 of the lamina into several Hnear segments with obtuse or in some 

 cases more pointed apices. Heer draws attention to the re- 

 semblance between G. sihirica and G. plmipartiia from Wealden 

 rocks but, as he says, the venation is rather coarser in the Siberian 

 leaves and the segments are generally narrower in G. sihirica. 

 Fontaine in his description of Jurassic leaves from Oregon appa- 

 rently identical with Heer's G. sihirica states that G. Schnidtiana 

 is a smaller form of the same species^, but Ward^ points out that 

 as G. Schmidtiana is described on one page and G. sihirica is defined 

 on the following page the former designation must be preserved. 

 It may be urged that as the name sihirica is the more widely used 

 and famihar term, considerations of convenience should override 

 this meticulously strict interpretation of the rule of priority. A 

 revision of Heer's Siberian material would, I have no doubt, result 

 in the reduction of his specific terms; on comparing several 

 specimens in the Museums of Copenhagen and Stockholm with the 

 illustrations in the. Flora Fossilis Arctica I found that several of 

 the pubhshed figures are far from accurate. For the present the 

 most convenient course would seem to be the retention of Ginlc- 

 goites sihirica for leaves similar to some of the more deeply divided 

 forms of G. digitata and to G. pluripartita, but normally character- 

 ised by a lamina divided almost or quite to the base into oblong, 

 obtuse or more or less acute segments. Leaves of the G. sihirica 

 type, using the term in the wider sense and including Heer's 

 other species Ginkgo Schnidtiana and G. lepida, are fairly common 

 in Jurassic rocks and occur also in Cretaceous floras ; they are 

 recorded from Kimeridgian beds in Scotland* (fig. 641, A), 

 Jurassic strata in Siberia, China^ (described by Yokoyama as 



1 Heer (77) ii. p. 61. PI. vn. fig. 6 ; PI. ix. fig. 5 6; PI. xi. ; Heer (82) ii A. p. 16 



Pis. R'., V. 



2 Fontaine in Ward (05) B. p. 125, PI. xxxni. » Ibid. p. 126 (footnote). 

 * Seward (11=) p. 679, fig. 9, A. 



= Yoko3'ama (06) B. PI. vn. : Krasaer (05) PI. ii. fig. 5. 



