584 Correspondence — Dr, P. Martin Duncan, 



Mr. De Wilde states that if the hooklets were solid appendages 

 attached to tlie stem, he would not expect them to break away so 

 re^'ularly as they seem to have done, because he says the hooklets 

 are stoutest at their base. But he must remember that although this 

 be their thickest part, yet it is their weakest point in their relation to 

 the stem. As points in illustration — twigs torn from the stem of a 

 plant, naturally break close to their attachment with the stem, yet 

 this is also their thickest point; and the spines of the Prodiictce 

 found in our soft shales, are seen in most cases to be fractured close 

 to their attachment to the shell, owing to the pressure they have 

 sustained. But this fracturing of the spines by pressure is not 

 always regular in its distance from the organism, either in the Pro- 

 diictce or the coral in question, as some of my specimens in your 

 possession clearly show. There are several other considerations that 

 might be urged against the supposed articulation of the hooklets 

 upon tubercles, but the fear of encroaching too far upon your space 

 forbids me from entering upon them at present. 



John Young. 



HuNTERiAN Museum, Glasgow, 

 November 5, 1868. 



ON EETEROPRYLLIA. 



Sm^ — I have read Mr. J. Young's communication to the Geol. 

 Mag. concerning HeterophjUice and Mr. De Wilde's letter also. Mr. 

 Fielding's note must be satisfactory to the able artist who drew from 

 nature the tubercles and spines of Heterophyllia mirahilis, nobis for the 

 Phil. Trans, (not for the Proceedings, as Mr.' J. Young asserts), but 

 really the slightest possible examination of the specimens proves 

 that the appearance of irregular fracture of the spines is the excep- 

 tion, and that which I have described is the rule. The irregular 

 fracture has been produced by pressure, which has acted more upon 

 the base of the tubercles than upon the junction of the hooklets with 

 the tubercles. Probably some anchylosis had occurred and the joint 

 had been destroyed. 



I am content to abide by the decision I came to whilst the Retero- 

 phyllice in the Hunterian Museum of Glasgow were still called ^S^r- 

 pu/ce, and to consider H. Lijelli and E. mirahilis very interestingly 

 separate species. It is very remarkable that Mr. J. Young did not 

 favour science with an elaborate essay upon these very peculiar 

 corals long before their importance became manifest to his able 

 fellow geologist, Mr. J. Thomson, and to me. Perhaps the enormous 

 amount of work still required to be undergone amongst the compara- 

 tively unknown fossils of the Scottish Coal Field has frightened the 

 worthy sub-curator. I would beg of him to cheer up and to try just 

 " a wee " of original pala^ontological research. When he has de- 

 scribed one species, his criticisms upon the works of those who are 

 liard at work at Scotch fossils will be more appreciated. At present 

 his criticisms are long but not strong. — P. Martin Duncan. 



