660 PROFESSOR A. C. SEWARD ON 



fanciful suggestion was prompted by a photograph illustrating a new species of 

 Platycerium, recently described from Malaya by Dr Christ,* in which the longer and 

 deeply lobed fronds are almost identical with those of H. dichotoma, while the smaller 

 orbicular leaves may be compared with those represented in text-fig. 3 and in photo. 6, 

 PI. VI. In the recent genus Dipteris the stem is rooted in the ground and the fronds 

 are not markedly dimorphic, and it is to this genus rather than to Platycerium that 

 Hausmannia appears to be closely allied. The Bornholm species H Forchammeri 

 shows a degree of variation in the dissection of the lamina which illustrates the risk of 

 regarding such differences as characterise H. dichotoma and H. Buchii as necessarily 

 of specific rank. It would, however, be unjustifiable to unite forms so distinct as those 

 shown in fig. 14, PI. I., and photo. 6, PL VI., without the evidence of clearly marked 

 transitional fronds. The important point is, not so much the delimitation of specific 

 boundaries, a task on which the palseobotanist wastes much time, but the fact that the 

 genus Hausmannia played a prominent part in the Jurassic floras of Europe. There 

 can be little doubt that in the Malayan and Indian Dipteris we have a nearly related 

 fern, which is a direct descendant of Jurassic ancestors some of which played a part in 

 the flora of Culgower. Hausmannia is recorded from the Wealden of North Germany 

 by Dunker and Schenk : the fragment described from the English Wealden as 

 Dictyo'pliyllum Romeri Schenk.t and a specimen from the Bernissart beds of Belgium 

 referred to that species,^ are probably portions of Hausmannia leaves. The Lower 

 Cretaceous species Asplenium Forsteri Deb. and Ett. § is probably identical with H. 

 dichotoma. The fragment figured by Fontaine from the Lower Cretaceous Shasta 

 formation as ? Hausmannia californica || may be a piece of a Hausmannia frond ; it is 

 possible that the specimen described by the same author as Marchantites erectus 

 (Leek.) 1 from the Jurassic of Oregon is also referable to Hausmannia. 



Hausmannia Richteri sp. nov. (Figs. 18, 18 A, PI. I.) 



The small incomplete leaf shown in fig. 18 seems worthy of a distinctive name. 

 A similar form is described by Nathorst as Hausmannia crenata # * from the Rhaetic 

 of Scania, the type-specimen being refigured by Saporta ; ft other similar leaves are 

 represented by Zigno's Protorhipis asarifolia \\ from the Jurassic of Northern Italy, and 

 P. cordata Heer §§ from the Lower Cretaceous of Greenland. The orbicular Culgower 

 type is characterised by a somewhat irregularly crenulate margin and by the absence of 

 prominent main ribs. As seen in fig. 18 A, the lamina is divided by anastomosing 

 vrinlets into polygonal areas abutting on forked veins: the enlarged drawing is shown 

 with the upper end pointing downwards. A similar form of leaf is met with also in the 

 recent Dipteris conjugata.\\\ 



* Christ (09). t Seward (94), p. 140. J Seward (00 3 ), pi. iii. fig. 34. 



§ Debey and Ettingshausen (59), pi. ii. fig. 11. || Ward (05), pi. lxv. 



IT Ward (05), pi. vi. fig. 1, p. 53. ** Nathorst (86), pi. xi. fig. 4. 



tt Saporta (94), pi. xxii. fig. 12. {J Zigno (68), pi. ix. fig. 2. 



§§ Heer (eO), pi. iii. fig. 11. |||| Seward and Dale (01), pi. xlviii. fig. 23. 



