283 
decomposed, ferruginous ironstone nodule. The specimen measures roughly about eight 
inche.s by live and a half, without tlie shelly matter. Across the dorsal region, from the 
one rounded diagonal ridge to the othei", the shell measures at least five inches. This 
will give some idea of the great breadth attained by this species, and its general globose 
or gibbous outline. The umbones are very large, incurved, and quite anterior. J udging 
by the space occupied by matrix between the cardinal edges of the two valves, the 
ligament must have been of great dimensions and strength. The collection contains 
two examples of this species, that from which the foregoing notes are tahcu, and a 
smaller one, which is believed to represent the young condition of the species. The 
latter, when held in certain lights, shows indistinct traces of radiating strise in the cast. 
Upon examining a remarhably fine specimen in the late Count Strzelecki’s Collec- 
tion, I find that it also, where the shelly matter is worn off, exhibits similar radiating 
ridges. In the paper on the Bowen Biver Coal Field Fossils I overlooked the fact that 
Prof. J. D. Dana had already called attention* * to the identity of his Cleolis grandis and 
Pachydomus globosus, Morris. 
My Colleague has obtained a specimen, denuded of all external shelly matter, 
from the Gympie Gold Field, which, although small, may be an individual of the 
present species ; it is, however, too imperfect to name definitely. 
Loc. and Horizon. Pelican Creek, Bowen Fiver, half-a-miln above Sonoma Poad- 
crossing, in a highly fossilifcrous concretionary and ferruginous mudstone ; Pelican 
Creek, in a sandstone above the Garrick Coal-seam — both horizons in the Middle or Marine 
Series, Bowen River Coal Field {B. L. JacTd). 
Genus — MHSONIA, Dana, 1847. 
Mymia, Dana, American Joiim. Soi., 1847, iv., p. 168. 
Maionia, Dana, Geology Wilkes’ U. S. Explor. Exped., Vol. x., 1849, p. 694. 
Ols. This genus is provisionally used, pending a detailed examination of all 
these dubious Permo-Carboniferous Bivalves, for shells after the type of M. elongata, 
Dana, and M. carinata, Morris, ,sp. The muscular system of the latter is quite different 
to that of various genera in which it has been placed, and accords better, although not 
exactly, with the characters of Mceonia as laid down by Dana in his latter description. 
MiEoiriA CARINATA, Morris, sp. 
Pa.chydomus carinatiis, Morris, Strzelecki’s Phys. Descrip. N. S. Wales, 1845, ir. 273, t. 11, f. 3 and 4. 
('ypHcardia rugulom, Dana, American Journ, Sci., 1847, iv., p. 157. 
Pachydomus caniMtus, McCoy, Ann. and Mag. Nat. Hist., 1847, xx., p. 301. 
Mwonia 7 carinata, Dana, Geology Wilkes’ U. S. Explor. Exped., p. 696, Atlas, t. 6, f. In and h. 
Pleurophorus ? carinatus, De Koninck, Poss. Pal. Nouv.-Galles dn Snd, 1877, 1*1. 3, p. 283, t. 19, f. 8. 
Pachydotims I carinatua, Etheridge fit, Proc. fl. Phys. Soo. Edinb., 1880, v., p. 300, t. 16, f. 53. 
^otomya (Mccimia) elongata, Eattc (non Dana), Proc. Linn. Soc. N. S. Wales, 1887, ii., Pt. 1, p. 139, t. 3. 
Ohs. The strongly marked umbonal ridge, and the slightly concave posterior 
®iope, at once mark this species as peculiar. Two specimens in a moderately good state 
preservation w'ere obtained in the Bowen River Coal Field ; both have the entire 
shell removed, and are therefore in the form of easts, but with the exception of some 
®hght displacement of the valves, the general outline is retained. I formerly placed 
this species in Pachydomns, but both this reference and Prof. De Koninck s to the 
genus PleuropTiorus I now believe to be erroneous. The shell does not coincide with the 
original types of Paehydomus, such as P. anliguatus and P. cuneatus.\ With regard to 
* American .7 ourn. Sci., 1848, v. , p. 433. . 
+ Mcgadesmus, J. de C. Sowerby, in Mitchell’s Three Expeds. Int. E. Australia, 1838, i., p. 16, 1. 1, 
* '2 and 3. 
