ARCIDiE. 129 



Barrois adopted Meek and Worthen's name Carbonarca for a shell from the 

 Carboniferous series of Spain, G. Gortazari. He describes it as having oblique teeth 

 in front and parallel teeth posteriorly, and therefore it differs from the diagnosis 

 of Carbonarca as laid down by the authors of that genus, 1 which is " cardinal margin 

 a little arched, with, at the anterior extremity in each valve, two rather oblique, 

 comparatively stout teeth, and extending along its entire length, from immediately 

 behind these, a row of minute interlocking teeth or crenulations, as in Area." 



De Koninck describes forty-three species of Parallelodon from the Carboni- 

 ferous Limestone of Belgium, twenty-eight of which are new, four of the new 

 species being founded on single specimens. He was, however, mistaken in placing 

 the GuculJxa arguta of Phillips in this genus, to which it has no affinity whatever. 

 The genus Omalia was invented by de Ryckholt (1853) to receive a number of 

 uncertain species that had been placed under various genera (Modiola, Avicula, 

 Pullastra, Cypricardia, Mya, Venus, Venerupis, and Pterinea) at different times. 

 Modiula amygdalina, Phillips, from the Devonian strata, heads this heterogeneous 

 list, and therefore there is no question of the name standing for those shells 

 which, having a place lower down the list, do not conform to the type. I am not 

 aware that any one of the shells mentioned possesses the peculiar generic 

 characters affirmed of it. 



Four of the species which I now refer to Parallelodon are included in this list — 

 Pullastra bistriata, M'Coy ; Modiola squamifera, Phillips ; Modiola concinua, M'Coy ; 

 and Venerupis cingulatus, M'Coy. The diagnosis given for the genus Omalia 

 (p. 73) is quite unsuitable for these shells, being — " Ces coquilles sont depourvues 

 de dents a la charniere 5 que le ligament est interieure, .... que les impressions 

 palleales, d'ailleurs assez superficielles, montrent un sinus non anguleux, 

 comparativement profond," &c. 



I am in doubt as to whether some or all of the species described as Cypri- 

 cardinia by Hall, 2 from the Devonian beds, should not really be referred to 

 Parallelodon. Several shells figured by him bear a close resemblance to P. 

 bistriatus, which de Koninck has shown to possess the characteristic hinge. The 

 date of Cypricardinia is 1859, and the name would therefore take precedence of 

 Parallelodon. Cypricardinia scalaris of the Devonian of Devonshire resembles 

 P. cingulatus very closely. All that Hall says of the hinge of this genus is, 

 " Hinge-line marked by a long fold or lateral tooth in one valve ; cardinal teeth 

 not determined." Fischer does not place the genus Cypricardinia in any family ; 

 but, comparing the figured species with P. bistriatus and P. cingulatus, it seems 

 to me that the Arcidse is the proper group for them to be placed in. 



It is interesting, from an evolutionist's point of view, to note that the striated 

 hinge-plates of some of the Aviculidse and Mytilidse (Myalina, Naiadites, &c.) are 



1 ' Geol. Surv. Illinois,' vol. vi, 1S75, p. 530. 



2 ' Geol. Surv. N. York : Palaeontology,' vol. iii, 1859, p. 2C6. 



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