Mimachlamys grossiana Iredale, 1939
IREDALE, T. 1939. Mollusca. Part 1. In: Great Barrier Reef Expedition 1928-29, B.M.(N.H.), Scientific Reports, 5 (6): 209-425, pls. 1-7. [p. 352, pl. 5, figs. 23, 23a]
Mimachlamys grossiana sp. nov. (Plate V, figs. 23, 23a.)
Shell rather small, longer than broad, nearly equilateral, subequivalve, of medium convexity, ears very unequal. The sculpture is less pronounced than in other members of this genus, and immature specimens generally lack all the prickly sculpture, though in the adult the major ribs bear small distant prickles. The beginnings of the valves are smooth; these are succeeded by plain radial riblets, the intervals between being finely obliquely radially scratched and minor riblets soon appearing. These minor riblets soon multiply, the minute scratching becoming finer and finer, until it disappears. The major riblets persevere, a little stronger than the minor ones which fill the interstices, and on these major riblets small prickles appear, placed far apart. On the right valve these major riblets number about fifteen, there being from three to six minor ones between each major one; all the riblets are flattened. The major riblets are more numerous on the left valve, up to thirty being counted, with only one or two minor ones between. The prickles are also placed nearer together. The external coloration is red, mottled with black, but internally the coloration is a pale reddish fawn, the edges of the shell internally being dark brownish red. Sometimes there is a red-brown patch in the centre of the shell inside. The anterior ears are large, the posterior very small, the anterior auricle of the right valve being strongly sculptured with five coarse ribs, the other ears all being finely sculptured. The byssal sinus is very large, the ctenolium rather short, but the teeth stout; no auricular crura, but the ears appear to gape a little. The cardinal crura are indistinct, a ridge running along each side subparallel to the hinge line; the latter is microscopically striate, but the crura themselves appear smooth. The edges of the shells irregularly crenulate and sharp, not regularly toothed, as in most species in this group. A small valve and a larger broken valve were picked out of the 9-12 fathoms' dredging off Low Isles, but the type flgured is a beautiful specimen collected by that energetic conchologist, Mr. George Gross, on Stradbroke Island, Moreton Bay, Queensland. Its measurements are: Length 44mm., breadth 40 mm., depth of valves 14 mm.
A very similar shell, in the Australian Museum collection from New Caledonia, is named Pecten squamosus Gmelin var. hybridus Lamarck. It is impossible to use Lamarck's name, as it is merely a usage of Gmelin's O. hybrida, with which he incorporated Gmelin's O. squamosa. Gmelin introduced his Ostrea hybrida ('Syst. Nat.' VI, p. 3318, 1791) for a shell from the Norwegian Seas, citing 'List. Conch.' t. 173, fig. 10, and 'Chemn. Conch.' VII, t. 63, figs. 601, 602, neither of which have anything to do with the tropical species under notice. The same species, even very similar specimens, was named by E. A. Smith, of the British Museum, Pecten serratus Sowerby from New Caledonia, but the shells look much more like P. irregularis Sowerby, figured on the same plate. Melvill and Standen (p. 183) recorded Pecten cuneatus Reeve from Torres Straits, and there appears to be confusion with irregularis Sowerby, serratus Sowerby and, squamosus Gmelin. Gmelin's Ostrea squamosa, ('Syst. Nat.' VI, p. 3319, 1791) was based on " 'List. Conch.' t. 184, fig. 21", from unknown locality. Dillwyn ('Index Hist. Conch. Lister', p. 14, 1823) has commented: "The Ostrea No. 35 of Schroeter and both the Ostrea squamosa and the Ostrea anonyma of Gmelin have been derived from this figure, which is considered by Lamarck to be a variety of Ostrea hybrida; these two of Gmelin's species, and this figure, have been erroneously quoted in the Descriptive Catalogue for Ostrea pellucens." Dautzenberg and Bavay ('Siboga Exped.' LXI, mon. liiib, p. 140 (14), December, 1911) used Pecten squamosus Gmelin, but overlooked the citation of Ostrea anonyma Gmelin ('Syst. Nat.' VI, p. 3329, 1791) as a synonym, though it had been provided for the same figure of Lister, even as Dillwyn had recorded. They regarded as synonymous, however, Ostrea sauciata Gmelin (VI, p. 3328, 1791, for 'Chemn. Conch.' VII, t. 69, fig. H: Red Sea), Pecten serratus Sowerby ('Thes. Conch.' I, p. 69, pl. xiii, fig. 56, 1842: Philippine Islands), Pecten larvatus Reeve ('Conch. Icon.' VIII, pl. xxxiv, sp. 158, figs. 158, 165, August, 1853 : Philippine Islands), and Pecten dissimilis Fischer ('Jonrn. de Conch.' VII, p. 341, June, 1859, en Montrouzier MS.: new name fot Pecten serratus Sowerby). In the same place Pecten irregularis Sowerby ('Thes. Conch.' I, p. 69, pl.xiii, figs. 51 and 52, 1842: no locality) was allowed as a valid species, Reeve's P. lemniscatus ('Conch. Icon.' VIII, pl. xxxv, fig. 170, August, 1853, as Ientiginosus: no locality; name altered in Index) being added as a variety. The tropical species known as P. lividus was determined as squamosus, the true lividus Lamarck having been described from South-West Australia. A form of lividus Lamarck (i. e. Scaeochlamys) reaches into southern Queensland as far north as Port Curtis, but this has nothing to do with the species now being dealt with, which might be associated with any of the other names quoted above except lemniscatus. The true lividus has always a heavy scaly sculpture on the ribs of the left valve, which is not seen in any of the figures cited above. Consequently the names must be allotted geographically, and squamosus Gmelin must be determined from the figure, and certainly it is not applicable to an Australian shell. Gmelin's sauciata must be relegated to the Red Sea, and Pecten serratus Sowerby, Pecten larvatus Reeve and Pecten dissimilis Fischer all refer to a Philippine Islands species, the first-named being preoccupied, and if larvatus Reeve be the same, that name anticipated Fischer's dissimilis, which is applicable only to the Philippine Islands shell, but is invalid through Fleming's P. dissimilis ('Hist. Brit. Anim.' p. 387, 1828). TOM IREDALE, 1939
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T. Iredale, 1939, plate 5.
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