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,' 

 pi. xxvii, figs. 2, 20, p. 347) has all the appearances of Anthracomya WilUamsoni 

 (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 [Pleurophorus 

 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 costre " — a character well seen in Anthracomya WilUamsoni. 

 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 scales in the same situation as obtains in 

 Anthracomya. I consider that the AnthracomyEe possess a set of characters 

 which is an approach nearer to the Mytilidas than Carbonicola, which again is 

 intermediate between the AnthracomyaB 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 

 Unionidaa. 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 limule and tooth-socket in Carbonicola, — all seem to show 



