GASTEROPOD FAUNA IN THE MILLSTONE GRIT OF SCOTLAND. 341 



The species has somewhat the characters of the ornament of A. Murchisoni; the 

 obliquity of the valve and the deep posterior ear are not characteristic of that species. 

 In A. Murchisoni, the right valve is flattened, and the ribs are much less nodular than 

 in the left valve. 



Aviculopecten regularis, sp. nov. (PL 1. figs. 2, 3.) 



Specific Characters. — Shell of moderate size, the left valve gibbose, the right 

 flattened. The body of the valve triangular, the lower margin broadly rounded. The 

 hinge line straight, equal in length to the greatest transverse diameter. Umbones 

 small, pointed, subcentral. The ears are depressed, especially the anterior ; the posterior 

 has its upper margin produced to a point, and its posterior margin falcate. 



Exterior. — The right valve has its anterior ear radially ribbed and its posterior 

 almost smooth, but almost obsolete distant radiating lines can be seen with a microscope. 

 The rest of the valve has fine flattened, close radiating ribs, becoming thicker as they 

 approach the margin. The left valve has coarse, raised linear ribs ; between each pair, 

 fine secondary ribs appear towards the inferior margin. Concentric lines of growth are 

 visible in the umbonal region. The ears of the left valve are not well seen. 



Dimensions. — PI. I. fig. 3. Specimen No. T4514 B measures: antero-posteriorly, 

 16 mm. ; dorso-ventrally, 13 mm. 



Locality. — Midlothian, Bilston Burn near Polton, bed 27 to 30 feet above the 

 Castlecary Limestone. 



Observations. — Two specimens, a right and a left valve, which I think belong to 

 each other, have been obtained, neither of which is, unfortunately, perfect. The marking 

 of the left valve is well preserved. I have been unable to refer the specimens to any 

 described species, and I have been obliged to consider it as a new species. 



? Aviculopecten neglectus, Geinitz, sp., 1866. (PI. I. figs. 4-7.) 



Pecten neglectus, Geinitz, 1866, Garb, tmd Dyas in Nebraska, p. 33, T. ii. fig. 17. 

 Aviculopecten neglectus, Meek, 1867, Amer. Journ. Sci. and Arts, vol. xliv., sec. ser., p. 183. 



„ „ Meek, 1872, Fin. Rep. U.S. Geol. Surv. Nebraska, p. 193, pi. ix. fig. 1, a, b. 



„ ,, Meek and Worthen, 1873, Geol. Surv. Illinois, vol. v. p. 589, pi. 261, fig. 7. 



Specific Characters. — Shell small, its body subovate, acute, only moderately gibbose. 

 The margin is regularly rounded below. The hinge line straight, shorter than the 

 greatest transverse diameter. The umbo is small, pointed, not elevated, subcentral. 

 The anterior ear in the right valve is small and flattened, triangular, separated from the 

 body of the valve by a groove and notch. It is ornamented by strong radiating ribs. 

 The posterior ear is triangular, depressed, with fine radiating markings, its margin 

 falcate. 



Exterior. — The right valve has its body almost smooth, with fine concentric 

 markings. The left valve is almost smooth in its juvenile condition, but becomes 



