Thracia meridionalis E. A. Smith 1885

“Thracia meridionalis, n. sp. (Pl. VI. figs. 4-4b).

Testa paulo inæquilateralis, modice convexa, ovato-oblonga, postice truncata, carinam obsoletam ab umbonibus ad extremitatem posticam exhibens, sordide albida, lineis incrementi rugosis, striisque tenuibus concentrice sculpta, undique minute grano-scobinata; margo dorsi antice valde declivis, aliquanto arcuatus, postice brevior, minus descendens, rectiusculus; margo ventris levissime excurvatus, utrinque parum adscendens. Latus anticum rotundatum, posticum oblique, vix arcuatim truncatum. Cardo, cicatrices et palli sinus fere ut in Thracia truncata (Brown).

This species is of an oblong form, rounded in front and squarely truncated posteriorly. It is slightly inequilateral, the anterior side being a trifle the longer. It is moderately convex, depressed or a little concave behind, a faint angulation extending from the umbones to the lower posterior end, thin, dirty whitish, finely concentrically striated, marked with more distinct lines of growth here and there, and everywhere very minutely roughened or subgranulated. The dorsal line is very oblique and moderately arched anteriorly, less descending and rectilinear behind, forming with the side margin, which is almost straight, and slopes inward or towards the middle of the slightly curved lower margin, a rather sharp angle. The hinge is not quite like that of Thracia truncata of Brown, the process to which the ligament attaches itself being rather slighter, distinct from, and soldered to the hinge-line. The muscular scars and the sinus in the pallial line are similar.

Length 23 mm., height 19, diameter 10.

Length 23 mm., height 18, diameter 9 ⅔.

Habitat.—Royal Sound, Kerguelen Island, in 20 to 60 fathoms; Betsy Cove, in 20 to 25 fathoms; Marion Island, in 50 to 75 fathoms; and Prince Edward Island, in 100 to 150 fathoms.

This is the southern representative of the Greenlandic species Thracia truncata, and indeed differs so slightly from it that it is with considerable hesitation I venture to describe it as distinct, being mainly influenced to do so by the difference of locality. It is not so equilateral, has the ventral margin straighter, the posterior end more abruptly truncated, the extremity being at the upper angle, whilst in the boreal form the lower end is usually the most prominent. The hinder dorsal slope in the present species is a little reflexed or bent over in both valves, forming an indistinct area, which in Thracia truncate is scarely traceable. A more tangible difference is in the slighter shelly process which supports the ligament, being, as it were, a separate piece joined on to the hinge-line.”

(Smith, 1885: 68-69)