MOLrUSCA. — HEDLEY. 71 



state, for Tate writes of it that the byssal sinus lies altogether in 

 the left valve and is consequently very long and narrow. The 

 suture from the hole to the edge traces the path travelled by the 

 byssus of Foramelina. 



A French Jurassic fossil which united the hinge of Melina to 

 the perforation of Anomia, was described by D'Orbigny 1 as 

 Hypotrema. Resembling the Australian shell in this ecceutric 

 combination, it differed by being what its author termed 

 " pleuroconch," that is having a deep lower and a flat upper 

 valve. In D'Orbigny's opinion the perforation contained a 

 muscle, not a byssus as iu Foramelina. So though Hypotrema 

 is nearer than any other genus that I can find in literature to the 

 shell under review, it cannot be regarded as identical. 



Even more like the Australian shell is Pulvinites argentea, 

 Conrad, 2 from the Upper Cretaceous of the Mississippi Valley. 

 But the reference of Conrad's fossil to the genus Pulvinites is 

 doubtful. 



FOKAMEUNA EXEMPLA, Sp. IIOV. 



(Plate xi.-xii., figs. 6-7-8.) 



Shell equivalve, equilateral, large, flat, discoidal, margin 

 irregular in outline. Valves thick, composed of brittle, imbri- 

 cating lamella? which both include and are overlaid by a thin 

 membranous epidermis, where eroded of a silvery sheen, interior 

 a dark bronze. Perforation in the right valve about 10 mm. in 

 diameter, median and subumbonal, internally with a raised 

 margin, externally excavated as an oblique furrow ascending to 

 the vertex. From the margin of the perforation a suture leads 

 to the anterior extremity of the hinge plate. Byssus a dense 

 bundle of threads about half an inch long. Hinge line about 

 43 mm. long. Area much eroded above and traversed by about 

 twenty-two narrow ligamental grooves which slightly radiate 

 from above. Externally the hinge gapes when the valves are 

 closed as in Melina. Adductor small, subcircular, about its own 

 breadth below the perforation, Byssal retractor rather larger 

 than the adductor and immediately above it in the left valve. 

 Pallial margin entire, about half an inch within the ventral 

 margin. Height, 120 : length, 130 mm. 



1 D'Orbigny — Journ. de Conch., iv., 1853, p. 432, pi. 10- Fischer 



Man. Conch., 1886, p. 933, fig. 702. 



2 Conrad — Journ. Acad. Nat. Sci. Philad. (2), iii.. 1858, p. 333 p] 33 

 fig. 5 ; Op. cit., iv., 1860, p. 298, pi. 46, fig. 51. 



