6 ■ SIE WILLIAM DAWSON 



that they may either have been ova or spawn of some animal deposited in patches on 

 fronds or stems of aquatic plants, and with or without an investing sac, or they may have 

 been groups of sporocarps, covered or partially covered with an iudusium, and borne on 

 somewhat thick, fleshy stems. 



In the former case they could not have been deposited in sand, like the eggs of Natica, 

 or in masses like the spawn of frogs ; but they may have been the ova either of gastropod 

 mollusks or of crustaceans depositing their eggs in flat patches on vegetable or other bodies 

 in water. The variable size and form of the patches may be regarded as so far corre- 

 sponding with this view of their origin. 



If of vegetable origin they would probably be the sporocarps of some cryptogamous 

 plant of aquatic habitat rather than seeds of phaenogamous plants. On this supposition 

 the various forms and sizes might be explained by supposing different species or varieties 

 or accidental differences of preserA^ation. 



It was evident that these questions could be best settled by microscopic examination, 

 which I could not learn had been undertaken, except by Mr. Powrie, who states in a let- 

 ter communicated to me that he has examined specimens microscopically without any 

 result. None jof the specimens on the flags seemed in a condition to afford structure, but 

 those on the shales from Myreton seemed more promising. Having removed some of the 

 flat pellicles of these specimens, I found that, though extremely thin, they were perfectly 

 opaque, and by attempting to rub them down I merely succeeded in finding that they 

 consisted of three extremely thin layers, the two outer black and carbonaceous, the inner 

 amber-coloured and translucent. As opaque objects, however, the best specimens showed 

 a hexagonal cellular areolalion, and on comparing this with the surface of sporocarps of 

 Profosalvinia from Ohio and Brazil, I found the structures perfectly similar. This was so 

 far an indication of vegetable affinity, as I know of no crustacean or molluscan ova show- 

 ing such cellular areolation. Finally, having removed a few of the discs from the matrix, 

 these were boiled for some time in nitric acid, by which the outer coat was in part 

 removed, and the interior was softened and caused to swell. In this condition, when 

 broken up and examined in water, the middle layer resolved itself into what seemed to 

 be a mass of microspores, which were easily separated, though some of them seemed 

 inclined to adhere in stellar groups, or, as Prof. Penhallow subsequently made out, to be 

 connected with groups of thin-walled cells. These microspores are of a delicate yellow 

 colour, thin-walled, and in some cases showing a triangular mark similar lo that on 

 spores of Isoetes, etc. These results seemed sufficiently to settle the vegetable nature of 

 Parka and its probable relation to the sporocarps of Protosalvinia of the Erian of America. 



At this stage of the investigation I thought it well to call in the technical skill and 

 experience of my friend, Prof. Penhallow, that I might have his independent judgment in 

 the matter. Prof. Penhallow was so kind as to submit the specimens to careful micro- 

 scopical examination, and has furnished me with the results so fully and clearly detailed 

 in the second part of this paper. 



Two questions still remain. Are all the organisms referred to Parka of the same 

 nature ; and to which, if any, of the plants associated with it does it belong ? 



As to the first question, the specimens experimented upon were of the ordinary form, 

 in a hexagonal areolation, and constitute patches enclosed wholly or partially in an indu- 

 sium. They are perfectly similar to all the numerous specimens in the Kescobie and 



