MICEODICTYON 135 



Microdictyon Dunkeri (Schenk). 



1870. Pecopteris decipiens, Trautschold, Nouv. Mem. Soc. Nat. Moscou, 



vol. iii. p. 29, pl. xix. fig. 5. 



1871. Laccopteris Dunkeri, Schenk, Palaeontographica, xix. p. 219, pl. xxix. 



figs. 3-5. 



1874. Laccopteris Dunkeri, Schimper, Trait, pal. veg. vol. iii. p. 506. 

 Phlebopteris Dunkeri f Schenk ' ^laeontographica, xxni. p. 161. 



1875. \ Pl. xxvii. fig. 10. 

 Microdictyon Dunkeri \^ pi 



1878. Laccopteris Dunkeri, Hosius and von der Marck, Palaeontographica, 



xxvi. p. 208, xliv. fig. 192 and 193. 

 1888. Laccopteris Dunkeri, Velenovsky, Abh. k. bohm. Ges. "Wiss. p. 12, 



pl. ii. figs. 3-7. 



Type. Small pieces of leaves showing fertile segments. Originals 

 in the Collections of Berlin and Gottingen. 



Schenk defines the species as : "folia .... ? segmenta pinnati- 

 fida, Iacinia3 e basi latiore lineares sinu lato rotundato remotae 

 integrae patentissimae obtusae basi 5-6 mm. lato, sori biseriales 

 rotundi, sporangia receptaculo centrali affixa, nervi primarii validi, 

 secundarii angulo acuto egredientes dichotomi, ramuli repetito- 

 dichotomi." l 



In a later description of the same species Schenk expands this 

 definition, and we may adopt his amplified diagnosis as affording 

 an accurate description, so far as the imperfect material allows 2 : 



Leaf-segments deeply pinnatifid, the lobes entire, at right angles 

 to the rachis, linear, obtuse, approximate; midrib strong, secondary 

 veins given off at a right angle, and forming large meshes which 

 are occupied by a reticulum of smaller veins. 



Sori circular, in two rows, without indusia ; sporangia eight to 

 ten, vertical incomplete annulus ; spores tetrahedral. 



The figure of Pecopteris decipiens, Traut., represents a small piece 

 of a leaf-segment with the long straight divisions characteristic of 

 Microdictyon Dunkeri (Schenk). Some of these show traces of the 

 sori. There are no indications of any characters which would justify 

 the retention of Trautschold's species. The volume of the Nouv. 

 Mem. Soc. Nat. Moscou in which Trautschold's paper is published 

 has the date 1876, but the paper wrapper of a reprint in my 



1 Palaeontographica, vol. xix. p. 219. 



2 Ibid. vol. xxiii. p. 161. 



