60 CARBONIFEROUS LAMELLIBRANCHIATA. 



border ; but in addition the surface-marking is very typical. The subimbricate 

 appearance and demarcation of the lines of growth into bundles is not met with in 

 any other species. 



The original specimen is smaller than the one I figure, measuring only about 

 60 mm. in its antero-posterior diameter, and the anterior end is enveloped in 

 matrix ; but it shows the characteristically shaped posterior end, and the sub- 

 imbricated, widely separated primary lines of growth dividing the secondary 

 lines into bundles. 



There is ia well-marked specimen in the Griffith Collection of the Museum of 

 Science and Art, Dublin, evidently named by M'Coy, and doubtless forming part 

 of the material on which he founded the species, for that there was more than one 

 specimen is at any rate probable, because, although the anterior end of the figured 

 specimen is not exposed, he states, "Anterior end forming an obtuse lobe before 

 the beak." It was not M'Coy's practice to give more than one figure of 

 any of his species, and he seldom gives more than one view of any specimen, 

 except mere outlines to show contours, or magnified drawings of surface 

 ornamentation. 



It is a matter of regret that at present no specimens have been met with which 

 reveal any details of the hinge-apparatus or muscular scars. 



I think it very probable that Mytilus pernella of de Ryckholt belongs 

 to M'Coy's Mod. patula. The peculiar surface-marking is faithfully depicted in 

 de Ryckholt's figures, and the general tumidity of the shell is well indicated. 

 His description is " Coquille epaisse, allongee, ovale, un peu arquee, renflee ; sa 

 surface est couverte de gros plis saillants, inegalement espaces, sur lesquels 

 passent de fines lignes d'acroissement, &c." This species, obtained from Vise, is 

 not, however, noted or even given as a synonym by de Koninck in his last work, 

 and it is probable that the shell on which the description was based has entirely 

 disappeared. 



This species would appear to have a very local distribution, being only known 

 from the Carboniferous Limestone of the south of Ireland, and, if my surmise is 

 correct as to the true character of M. viacrocephala, very rarely in Belgium in 

 stage ii of the Carboniferous Limestone. 



MoDiOLA MEGALOBA, M'Goij, 1844. Plate II, figs. 5 — 10. 



MoDiOLA MEGALOBA, JI'Coi/, 18i4. A Sjnopsis of the Characters of the Carboni- 

 ferous Fossils of Ireland, p. 75, pi. xi, fig. 31. 

 Mtalina Foynesiaxa, Baily, 1860. Memoirs of the Greological Survey of Ireland, 



Explanation of Sheet 142, p. 13, fig. 4. 



