Mr Etheridge on Fossils from Boicen River Coalfield. 301 



Pachydomus globosus — J. de C. Sowerby. 



Megadesmus glohosKS, J. de C. Sow., Mitchell's "Three Exped. Int. E. Aus- 

 tralia," 1838, i., p. 15, t. 3, f. 1 and 2. 



Pachydomus ,, Morris, Strzelecki's "Phys. Descrip. N. S. Wales," 

 etc., 1845, p. 272, t. 10, f. 2 and 3. 



(?) ,, „ De Koninck, Foss. Pal. Nouv-GallesduSud., 1877, pt. 



3, p. 272, t. 18, f. 5. 

 ,, ,, Etheridge, jun.. Cat. Australian Foss., 1878, p. 75. 



Ohs. — The fossiliferous rock of Pelican Creek lias furnished 

 a ponderous example of this species, but in a wretched state 

 of preservation, without any trace of shelly matter remaining, 

 and the whole substance of the cast having assumed the form 

 of a decomposed feruginous ironstone nodule. The specimen 

 measures roughly about eight inches by five and a half with- 

 out the shelly matter. Across the dorsal region, from the 

 one rounded diagonal ridge to the other, the shell measures 

 at least five inches. This will give some idea of the gTeat 

 breadth attained by this species, and its general globose or 

 gibbous outline. The umbones are very large, incurved, and 

 quite anterior. Judging by the space occupied by matrix 

 between the cardinal edges of the two valves, the external liga- 

 ment must have been of great dimensions and strength. The 

 collection contains two examples of this species, that from 

 which the foregoing notes are taken, and a smaller one, which 

 I believe to represent the young condition of the species. 

 The latter, when held in certain lights, shows indistinct traces 

 of radiating striae in the cast. Upon examining the remark- 

 ably fine specimen figured by my friend Professor Morris, 

 r.G.S., in the late Count Strzelecki's work, I find that it also, 

 where the shelly matter is worn off, exhibits similar radiating 

 ridges. The latter specimen might almost stand for the 

 original of the figure, by Professor J. D. Dana, of his Mceonia 

 grandis* so close is the resemblance. To avoid any cause of 

 error in this matter, I sought the kind assistance of Professor 

 Morris, who at once pronounced the specimen in question, in 

 the Strzelecki Collection, to be his type of James de Carle 

 Sowerby's species Megadesmus glohosus, and it was then un- 

 questionably apparent both to Professor Morris and Dr H. 



* Geol. U.S. Exploring Exped., p, 696, t. 6, f. 7 and 7a, 8 and 8a. 



