Page:Quarterly Journal of the Geological Society of London, vol. 34.djvu/38

14 many years ago by Captain Thomas Brown as Avicula modioliforme; but as I cannot distinguish any characters, either external or internal, by which to specifically distinguish Captain Brown's shell from Dr. Fleming's, I propose to adopt the name given by the former as a varietal designation for the thinner and lighter form of M. crassa. To the synonymy already given must therefore be added:—

A specimen from Fifeshire obtained since my paper was written exhibits another character not hitherto figured, a series of minute pits (? muscular-fibre-pits) running from above the double umbonal anterior muscular scars along the edge of the thickened hinge-area backwards. This is also visible in a specimen from the Water of Leith which has lately come under my notice; but here the pits are shallower, wider, and further removed from the edge of the hinge-area.

''Loc. and Horizon''. Forming a bed of shale with Schizodus Salteri, above and below the shale with marine fossils, at Woodhall, as before.

, sp. nov. Pl. I. fig. 15, and Pl. II. figs. 16, 17.

''Sp. char.'' Trigonal; anterior side small, truncated, with a slightly sigmoidal margin, descending from the beak at rather less than a right angle; posterior end expanded, flattened, with its margin slightly convex or subtruncate. Hinge-line somewhat depressed, a little less than the width of the shell, the angle formed by the union of the hinge-line and posterior margin an obtuse one. Beaks sharp, terminal, curved anteriorly, with a slightly prominent sigmoidal ridge extending from each down the anterior side and close to its margin; ventral margin convex. Shell ornamented with concentric lines of growth.

Obs. This species may be compared with Mytilus Flemingii, M'Coy, Myalina lamellosa, De Kon. , Myalina perattenuata, Meek and Hayden, and M. meliniformis, Meek and Worthen ; but its greatest affinity is with the first two of these. From Mytilus Flemingii it may be distinguished by possessing a smaller and more truncated anterior end, the bounding ridge from the beaks being less posterior in position, a less-depressed and shorter hinge-line, and a more broadly rounded ventral margin. From Myalina lamellosa,