Ill 



PARKA 



39 



thickened discs of nearly constant size, visually 2 mm. in 

 diameter, and of variable number. The discs are isolated spore 

 masses, containing numerous cuticularised spores (Fig. 20, 3) of 

 wliieh there is no evidence that they were formed in tetrads, or 

 that they ^vere heterosporous. These discs ncAcr overlap, though 

 they coalesce occasionally. A grooved lamina (Fig. 20, 2) occiu-s 

 on one side of the thallus and is probably ventral. 



In general habit Don and Hickling compare Parka with the 



Fig. 20. Parka decipiens, Flem., from the Lower Old Red of Scotland: 

 (1) a large thallus (natural size); (2) the folded lamina (x2); (3) spores 

 ( X 150). After Don and Hickling (1917). 



Coralline Alga Melohesia (Lithophyllum) lichenoides, Ag. of the 

 Rhodophyceae (Fig. 21) and they conclude that the thallus 

 grew probabh^ attached to or on the surface of mud or sand. 



With regard to the all -important question of affinity, Don 

 and Hickling dissent entirely from the Dawsonian view that 

 Parka was a sporocarp of "a somewhat generalised plant, 

 shadowing forth the recent rhizocarps^," They regard it as a 

 very low spore-bearing plant, belonging to a group which 



^ Reid, Graham and jNIacnair (1897). 



