228 KILSSOIflA. 



1850. PteropJiyUum tenuicaule, Unger, Gen. spec, plant, loss. p. 291. 



1854. Pterophylhtm tenuicaule, Morris, Brit. Foss. p. 19. 



1864. Pterophylhtm mcdianum, Leckenby, Quart. Journ. Geol. Soc. vol. xx~ 



p. 77, pi. viii. fig. 3. 

 1864. Pterophyllwn tettttica/de, ibid. p. 76. 



P. angustifolium, ibid. p. 77, pi. viii. fig. 2. 

 1870. Dioonites mcdianus, Schimper, Trait, pal. veg. vol. ii. p. 148. 



D. angustifolius, ibid. 



1873. PttropkyUum mcdianum, Zigno, Flor. foss. Oolit. vol. ii. p. 24 r 

 pi. xxix. fig. 4. 



P. angustifolium, ibid. p. 26. 



P. tenuicaule, ibid. 

 1875. Pterophyllwn medianum, Phillips, Geol. Yorks. p. 226, ligu. 55. 



P. tenuicaule, ibid. p. 227, pi. vii. fig. 19. 



P. angustifolium, ibid. p. 227, lign. 56. 

 1892. Nilssonia mediana, Fox-Strangways, Tab. Foss. p. 139. 



JV. angustifolia, ibid. p. 138. 



N. tenuicaulis, ibid. p. 139. 



Type-specimens. The type-specimens of PteropJiyUum medianum, 

 Leckenby, ex Bean MS., and of P. angustifolium, Leek., ex Bean 

 MS., are in the Leckenby Collection, Cambridge (JS"os. 278, 275). 



Frond broadly linear ; the lamina is divided into numerous 

 linear segments of unequal breadth traversed by several parallel 

 veins. This species agrees closely in habit with Nilssonia compta, 

 but differs in the narrower leaf - segments and in their more 

 acuminate and less truncate apices. The veins are somewhat less 

 prominent in Nilssonia mediana, and the lamina is thinner and 

 not so stout as in N. compta. 



The specimen figured by Phillips in 1829 as Cycadites tenuicaulis 

 from the middle shale of Gristhorpe is defined as follows in the 

 third edition of the Geology of Yorkshire: "Frond lanceolate, 

 ample, with a slender rachis ; leaflets perpendicular to the rachis, 

 unequal, ending obtusely, approximate at the base ; venation 

 parallel, delicate." J 



In 1864 Leckenby described two species of Yorkshire Oolite 

 plants under the names PteropJiyUum medianum ami P. angustifolium; 

 the type- specimens of these species are, I believe, indistinguishable 

 specifically from the plant named by Phillips Cycadites tenuicaulis. 

 According to the strict rules of priority Phillips' term should be 



Phillips (75), p. 227. 



