Fresidenfs Address. 49 



will be found to differ more or less from the existing 

 species. 



Modiola is well represented by a large shell, M. litho- 

 domoides (Etheridge),* which it is quite probable may turn 

 out to be only the full-grown variety of Modiola lingucdis 

 (Phillips). Four other species, in addition to the two men- 

 tioned, occur in Scotch Carboniferous strata. Professor 

 M'Coy has described a bivalve, with apparently all tlie 

 characters of the recent Lithodomus, from the Carboniferous 

 beds of Northumberland, and it is also found in the Lingula 

 ironstone at Carluke.-|- 



From their resemblance to the Dreissenidai I believe it 

 quite possible for Anthraco'ptera and Anthracomya to belong 

 to this family rather than to the Mytilidm. The two genera 

 are almost entirely restricted to the brackish- water strata of 

 the Carboniferous, the Coal Measures, the Middle Coal and 

 Iron series, and portions of the Calciferous Sandstone series. 

 In certain places they must have swarmed in great numbers, 

 and with another genus, Anthracosia, have formed what are 

 now moderately thick and compact beds. Anthracoptera in 

 outline and form greatly resembles Myalina, but there is no 

 trace of the striated hinge-plate of this genus, or in fact 

 of any hinge-plate at all. J The genus was published by Dr 

 Dawson, in Canada, under the name of Naiaditcs,^ on speci- 

 mens obtained from the Coal Measures of the South Joggins, 

 ISTova Scotia. The affinity of these shells has been discussed 

 by Dr Dawson at some length. He considers them to be 

 brackish-water shells, allied to the Mytilidcc, or embryonic 

 forms of Unionidee, and states that the structure of the shell 

 is similar to that of the latter family. || There is an internal 

 lamellar layer, a subnacreous layer of vertical prismatic 

 shell, and an epidermis ; an external ligament and a byssus. 

 Dr Dawson concludes, " The mode of their occurrence pre- 

 cludes the idea that they were burrowers, but favours the 



* " On some Undescribed Carboniferous Fossils" (Geol. Mag., 1875, ii., 

 p. 241). 



t Armstrong and Young, Cat. AV. Scot. Foss. , p. 54. 



X Salter, Mem. Geol. Survey, Great Britain, Country around Wigan, 1862, 

 p. 37. 



§ Acadian Geology, p. 202. II Ihid., p. 203, 



VOL. VII. D 



