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:—
| Avicula modioliforme, | Brown, Foss. Conchology, 1849, p. 162,
pl. 66. fig. 19. |
| „„ | Morris, Cat. Brit. Foss. 1854, 2nd ed.,
p. 162. |
| „„ | Salter, Mem. Geol. Survey Scotl. No. 32,
1861, p. 146. |
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.
Myalina sublamellosa, 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[1], Myalina lamellosa, De Kon.[2], Myalina perattenuata, Meek and Hayden[3], and M. meliniformis, Meek and Worthen[4]; 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,
