ANTHRACOMYA. 87 
is necessary to point out in what manner the characters of Cyclas (Cyrena) differ 
from Anthracomya. 
Cyclas is suborbicular in shape, nearly equilateral, and possesses as dentition 
cardinal teeth 2—1, lateral teeth 1—1 : 2—2; while Cyrena has three cardinal 
teeth and a slightly sinuated pallial line. 
The shell figured as Pleurophorus by Meek and Worthen (‘ Geol. of Illinois,’ 
pl. xxvii, figs. 2, 20, p. 347) has all the appearances of Anthracomya Wialliamsoni 
(Brown). In the figure the position of the accessory-anterior-adductor scar is 
well shown, and the authors remark on the different situation of this scar in 
King’s Pleurophorus. “It evidently differs from that species [Plewrophorus 
costatus, Brown, from the Permian] in having the scars of its pedal muscles 
nearly marginal and placed directly over those of the anterior adductors, instead 
of partly behind them.’ The surface of casts is said to show ‘‘ traces of a few 
obscure concentric markings crossed on the posterior dorsal region by three 
obscure radiating coste”—a character well seen in Anthracomya Williamsoni. 
The description and figures are perfectly typical, and I have no doubt as to the 
nature of the shell. 
The paleontologists of the Irish Geological Survey did not accept Mr. Salter’s 
genus Anthracomya, but referred their specimens to Anthracosia and Myacites. 
The Irish specimens are unfortunately not in the best state of preservation, but 
they exhibit characteristic features and are separated from Myacites at once by 
the absence of a sinuated pallial sinus. 
Anthracomya and Carbonicola (the Anthracosia of previous writers) are no 
doubt closely related, but they are easily distinguished from one another by the 
absence, in Anthracomya, of the characteristic hinge-plate or hinge-teeth of 
Carbonicola, and by the typical expanded and broad posterior end which always 
obtains in this genus. It is noteworthy that a large number of Lamellibranch 
shells occurring with an undoubtedly marine fauna in Carboniferous rocks possess 
this last character; I refer to the genus now known as Sanguinolites, and this 
genus has the accessory-pedal muscle scars in the same situation as obtains in 
Anthracomya. I consider that the Anthracomyz possess a set of characters 
which is an approach nearer to the Mytilide than Carbonicola, which again is 
intermediate between the Anthracomyz and the modern Unios. 
The position of the accessory-adductor muscle-scar in both Carbonicola and 
Anthracomya has rather a Mytiliform arrangement, more than occurs in recent 
Unionide. The traces of an obsolete byssal sinus in Carbonicola, more 
conspicuous also in Anthracomya; the tendency in the species of Carbonicola to 
have a truncate posterior end, and the universal occurrence of an expanded and 
truncate termination, with an oblique diagonal ridge, in Anthracomya; the 
longitudinally striated lunule and tooth-socket in Carbonicola,—all seem to show 
