BIVALVIA. 81 
Oppel (‘ Juraformation’) has made the Cornbrash shell into a new species, with the name of 
Panopea Haueri ; 1 can, however, with confidence state that there is no evidence that the 
fossil in question has ever been obtained in Yorkshire lower than the Cornbrash; in 
Gloucestershire its lowest position is at the base of the Great Oolite. 
Myacires recurvum, Péil., sp. Tab. XXXVI, figs. 4, 4 a. 
AMPHIDESMA RECURVUM, Phil. Geol. York., i, pl. 5, fig. 25. 
Lurrarta sinvosa, Roemer, Ool., tab. 19, fig. 24, Nachtr., p. 42. 
PLEUROMYA RECURVA, dg. Et. Orét. Myes., p. 234 et p. 246, t. 29, fig. 9. 
Lyonsia REcURVA, D’Orb.? Prodr., 12 ét., No. 123. 
Myacires recurva, Mor. Cat. Brit. Foss., 1854, p. 214. 
AMPHIDESMA RECURVUM, Bean. Mag. of Nat. Hist., 1839. 
MyacirEs recurvuM, Leckenby. Proc. Geol. Soc., vol. xv. 
Testa elongato-trapeziformi plano-convexa concentrice striato-rugosa antice brevissima 
oblique truncata bast perarcuata posterius producta dorso antice sinuatim depressa, margine 
cardinali postico sinuato, umbontbus crassis incurvis. (Roemer.) 
Shell a lengthened trapeziform, moderately convex, with large, concentric, rugose_pli- 
cations ; anterior side very short, obliquely truncated ; base curved elliptically ; the posterior 
side produced, compressed, close-fitting; the superior margin somewhat sinuated or 
concave ; the umbones elevated, pointed, and incurved. Usually the anterior side has a 
furrow, which passes from the umbones downwards perpendicularly or slightly directed 
forwards to the inferior border, but in some of the more gibbose specimens it cannot be 
distinguished. The test is delicate; the ornamentation of the surface has the radiating 
lines of granules so dense and minute, that they can only be distinguished by the aid of a 
considerable magnifying power. The height is two thirds of the length, the diameter 
through the valves being equal to half the length. These dimensions apply to the shorter 
Cornbrash examples, but many of the Kelloway Rock specimens are more elongated. To 
the latter variety may be attributed the Zutraria sinuosa, Roemer ; it is necessary, however, 
to separate altogether the Lutraria recurva, Goldf. (‘ Petref.,’ tab. cliii, fig. 15), which has 
the general figure very different. The example of Agassiz is unusually short and gibbose ; 
and as he has figured a cast, we are precluded from comparing the ornamentation of the 
surface. D’Orbigny (‘ Prodrome,’ i, p. 359) has separated it under the title of Panopea 
subrecurva ; but, considering the varieties of figure which this species assumes, probably it 
is only a short variety of the species of Professor Phillips. 
Myacites recurvum possesses so little of the aspect of a Gresslya (Lyonsia, D’Orb.) 
that we are led to speculate upon the probability that Lyonsia recurva, D’Orbigny, is a 
form erroneously ascribed by that author to the species in question. 
Geological Positions and Localities. Myacites recurvum is almost peculiar to the 
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