BIVALVIA. 81 



Oppel (' Juraformation') has made the Cornbrash shell into a new species, with the name of 

 Panojpea Hauerl ; I 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. 



Myacites recurvum, Phil., sp. Tab. XXXVI, figs. 4, 4 a. 



Amphidesma EECURVU5I, Phil. Geol. York., i, pi. 5, fig. 25. 

 LuTRARiA siNUOSA, Roemer. Ool., tab. 19, fig. 24, Nachtr., p. 42. 

 Pleuromya recukva, Ag. Et. Cret. Myes., p. 234 et p. 246, t. 29, fig. 9. 

 Lyonsia recurva, D'Orb.f. Prodr., 12 6t., No. 123. 

 Myacites recukva, Mor. Cat. Brit. Foss., 1854, p. 214. 

 Amphidesma recurvum. Bean. Mag. of Nat. Hist., 1839. 

 Myacites recurvum, Leckenby. Free. Geol. Soc, vol. xv. 



Testa eIon(/ato-trapcziformi piano- convex a concentrice striato-rngosa antice brevissima 

 oblique truncafa hasi perarcuata posterius producta dorso antice sinuatim depressa, maryine 

 cardinali postico sinuato, umbonibus 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 umboues 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 

 tlirougli 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 Lutraria 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 Fanopea 

 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 Gresslj/a (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 



11 



