Geological Society, 599 



Occurs both as fasciculate and as massive colonies. The chief dis- 

 tinguishing featm-es of the genus are the wide extrathecal area, 

 large dissepiments, complex central column, and horizontal and 

 widely-spaced tabulse. Lonsclaleia is an Avonian or Lower Car- 

 boniferous genus, especially abundant in the highest horizons of 

 that series (D.^ and higher beds). The earliest example is 

 Lonsdaleia prcBnunfin, from the Si/rin^otJii/ris Zone (C). 



A number of species and local forms have been recognized and 

 are described. 



May 12th, 1915.— Dr. A. Smith Woodward, F.R.S., President, 

 in the Chair. 



The following communication was read : — 



' On Parka decipiens Fleming.' By George Hickling, D.Sc, 

 F.G.S., and Aa-chibald W. R. Don, B.A., F.G.S. 



The paper is a joint statement of originally independent 

 investigations of this Old Red Sandstone organism. The views 

 of Fleming, Hugh Miller, Mantell, Lyell, Powrie, Page, and 

 others are quoted to illustrate the chequered career of this 

 enigmatical fossil in geological literature. To Dawson and Pen- 

 hallow, supported by Reid and MacNair, belongs the credit of 

 making the fii'st serious attempt to obtain definite evidence as 

 to its nature, and of establishing its vegetable character. The 

 present account is based on the observation of great numbers of 

 specunens in the field, and on tlie microscopic study of impression - 

 material, of thin sections, and of macerated material. 



The plant is most abundant in the Lower Old Red of the 

 Kincardine-Forfar-Perth area, where it is by far the commonest 

 fossil, especially in the shale-bands ; Parka is confined to the lower 

 two-thirds of the Caledonian Series. It is recorded from a few 

 other localities in Central Scotland, and also from the Upper 

 Ludlow and Lower Old Red of the ' Hereford ' area. 



The organism is shown to be a complete cellular thalloid plant, 

 agreeing generally in its vegetative structure with certain alga?, 

 but differing from all known algae in the production of cuti- 

 cularized spores. The thallus is closely set with subcircular 

 swellings (' discs'), each enclosing a mass of simple spores (homo- 

 sporous). An investing layer, probably one cell thick, of relatively 

 large cells surrounds the smaller-celled 'parenchyma' of the thallus. 

 The spore-masses are individually enclosed by the latter tissue, but 

 there is no indication of a specialized sporangial wall. The growth 

 of the plant is marginal and indefinite, and mature spores are 

 found in plants of all sizes — that is, so far as observed, in all plants 

 that are in a suitable state of preservation. The stinicture described 

 by previous writers as an ' indusium ' is interpreted as the ' sole ' of 

 the thallus in a more or less detached condition. While the general 

 structure and mode of growth of the plant make it very difficult to 

 place it higher than the Thallophyta, it must be recognized that 

 the organism is in some respects unique. 



