176 PERMIAN FOSSILS. 
Nucula Tateiana is with difficulty distinguished from the JV. gidéosa, Fleming, of 
the Carboniferous system: the former, however, differs from the latter in its anterior 
and posterior slopes being more inclined, and its umbones less tumid. From the 
Permian and Petschorian VV. Wymmensis, Keyserling, it differs in being nearly, or 
perhaps entirely, smooth, and not so compressed. 
Hahitat:: Humbleton Quarry, in Shell-limestone. 
Genus Leda, Schumacher. 
Diagnosis.—“ Shell equivalve, inequilateral, oblong, produced posteriorly, closed, 
smooth, or concentrically striated, invested by an epidermis; margins smooth; beaks 
approximated, incurved; inside more or less nacreous; hinge-line angulated, and 
formed, as well as the ligament, as in Vucula. Pallial impression with a sinus.””* 
Lepa VintTI,’ King. Plate XV, figs. 21, 22. 
Nucuxa VintI, King. De Verneuil, Bull. Soc. Geol. de France, 2™ série, vol. i, p. 32, 
1844. 
a mae es Geol. Russ., vol. i, p. 224, 1845. 
— — 45 Tennant, Strat. List, p. 88, 1847. 
LEDA — 4, King, Catalogue, p. 11, 1848. 
— — , Howse, Trans. T. N. F. C., vol. i, p. 248, 1848. 
NUCULA SPELUNCARIA, Geinitz. Versteinerungen, p. 9, pl. iv, fig. 6a, 6, 1848. 
Diagnosis.— Form a little nequilateral: aztercor end the shortest, and rounded : 
posterior end attenuated, and rounded at the extremity: wmbones rather tumid, and 
‘turned posteriorly : surface marked with slightly waved, prominent, transverse lines, 
which suddenly become nearly obsolete on the posterior third of the valves: pallal 
sinus very small.’”* 
The form of this elegant species indicates its generic position more than the 
character of its pallial line, which appears to be scarcely sinuated (Vide Pl. XV, 
fig. 22). It closely resembles the Muschelkalk Leda eaxcavata (Nucula id.) of Goldfuss, 
and appears to have some similarity to the imperfectly-known Permian Leda Kazanensis 
(Nucula id.) of De Verneuil. Leda parunculus (Nucula id.), Keyserling, is another allied 
shell, which is, however, more inequilateral than the present species. My largest 
specimen measures three quarters of an inch in width. 
Well-marked casts exhibit a faint but broad furrow (in the shell a ridge) running 
1 Forbes and Hanley, British Mollusca, vol. u, p. 226. 
2 Named after Mr. Robert Vint, of Sunderland, whose assistance in my early studies merits my warmest 
acknowledgments. 
8 King, Catalogue, p. 11. 
