176 PERMIAN FOSSILS. 



Nucula Tateiana is with difficulty distinguished from the N. gihhosa, 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 N. Wymmensis, Keyserling, it differs in being nearly, or 

 perhaps entirely, smooth, and not so compressed. 



Habitat: Humbleton Gluarry, 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 Nucula. Pallial impression with a sinus."^ 



Leda Vinti/ King. Plate XV, figs. 21, 22. 



Nucula Vinti, King. De Verneuil, Bull. Soc. Geol. de France, 2°"' s6rie, vol. i, p. 32, 



1844. 



— — „ Geol. Russ., vol. i, p. 224, 1845. 



— — „ Tennant, Strat. List, p. 88, 1847. 

 Leda — ,, King, Catalogue, p. 11, 1848. 



— — „ Howse, Trans. T. N. F. C, vol. i, p. 248, 1848. 

 Nucula speluncakia, Geinitz. Yersteinerungen, p. 9, pi. iv, fig. 6 a, b, 1848. 



Diagnosis. — " Form a little inequilateral : anterior end the shortest, and rounded : 

 posterior end attenuated, and rounded at the extremity : umbones 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 : pallial 

 '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 PI. XV, 

 fig. 22). It closely resembles the Muschelkalk Leda excavata {Nucula fc?.) of Goldfuss, 

 and appears to have some similarity to the imperfectly-known Permian Leda Kazanensis 

 {Nucula id.) of De Verneuil. Leda par unculus {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 MoUusca, vol. ii, p. 226. 



^ Named after Mr. Robert Vint, of Sunderland, whose assistance in my early studies merits my warmest 

 acknowledgments. 



'* King, Catalogue, p. 11. 



