BDMONDIA TRUNCATA. 1 & 



represents a freshwater stratum lias given rise to the view that W. punctatella might 

 have been either Garbonicola or Anthracomya. It has not the transverse shape, 

 with narrow anterior and broad posterior ends, of the latter genus, and the lines of 

 growth are coarser and more rugged than obtains in species of that genus. 

 Neither does the contour recall that of Garbonicola, though the coarser marking on 

 the surface is like that which obtains in this genus; but I do not know of any 

 species of the genus which has punctate markings. 



If the markings denote a prismatic structure in the outer layers of the shell, the 

 late Dr. John Young found that the prismatic cellular structure is confined to 

 shells belonging to the Aviculidse, or wing-shells, and the Mytilidae, or mussels. 

 He found it present in Pinna, Actinopteria, Posidonomya and Myalina. Quite 

 recently Mr. John Smith informs me that he has met with the structure in 

 Aviculopecten dissimilis. Dr. Young was unable to find prismatic structure in 

 Garbonicola, Anthracomya, and Naiadites. 



Bdmondia trunoata, sp. nov. Plate XXIV, figs. 6 — 8. 



Specific Characters. — Shell small, inequilateral, very moderately gibbose, oval. 

 The anterior end comparatively broad and shorter than the posterior, its margin 

 rounded. The lower margin slightly convex, the posterior blunt and rounded. The 

 hinge-line slightly arcuate. Umbones obtuse, small, very inconspicuous; placed in 

 the anterior third of the hinge-line. The valves are regularly convex, slightly 

 more so from above downwards than antero-posteriorly. Dorsal slope somewhat 

 compressed, no lunule or escutcheon. 



Interior. — The cast shows the groove beneath the hinge-plate for the peculiar 

 process characteristic of the genus. 



Exterior. — The surface is almost smooth, but fine concentric lines are to be seen 

 with a microscope. 



Dimensions. — PI. XXIV, fig. G, measures — 



Antero-posteriorly . . . .15 mm. 



Dorso-ventrally . . . .10 mm. 



Locality. — The lower Carboniferous beds of Glencartholm, Eskdale, Dumfries- 

 shire. 



Observations. — This little shell is not uncommon in the fossiliferous beds of 

 Glencartholm, which contain Lithodomus carbonarius, Hind, and Leiopteria divisa, 

 M'Coy, sp., shells which occur in the Calciferous Sandstone Series of Randerston, 

 Fife. The squat form and the absence of special ornament will serve to distinguish 

 the species. 



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