Mr. R. Etheridge on Carboniferous Lamellihranchiata. 101 



bonformation und Dyas in Nebraska '*, Dr. H. B. Geinitz has 

 figured, under the name of Nucula kasonensis^ De Vern. and 

 De Keys., a shell, one figure of which (fig. 34) also re- 

 sembles the present form ; however, the attenuated end (in 

 this figure) is too blunt, broad, and not sufficiently arcuated ; 

 it is also a much smaller shell. From L. hella striata, Stevens f, 

 L. Traqiiairii is distinguished by its greater anterior develop- 

 ment, more rounded ventral margin, and much greater gib- 

 bosity. 



Loc. and Horizon. From the brown sandstone of Knockhill 

 Quarry, Strathkinness, near St. Andrews; Cement-stone group 

 of the Lower Carboniferous series. Cabinet of Dr. Traquair, 

 after whom the species is named, also coll. Geol. Survey of 

 Scotland. 



Genus Leptodomus, M'Coy, 1844 

 (Synopsis Carb. Foss. Ireland, p. 66; redefined Brit. Pal. Foss. p. 277). 



Originally described in his work on the Carboniferous Lime- 

 stone Fossils of Ireland, this genus was afterwards redefined 

 by Prof. M'Coy, and in its emended form contained species 

 differing a good deal from those on which the genus was ori- 

 ginally founded. 



Leptodomus fragilis, M'Coy. PI. IV, figs. 5-7. 



Leptodomus fragilis, M'Coy, Syn. Carb. Foss. Ireland, 1844, p. 67, 

 t. 10. f. 11; Tennant, Strat. List Brit. Foss. 1847, p. 99 (without de- 

 scription) ; Morris, Oat. Brit. Foss. 18o4, 2nd ed. p. 206 (without 

 description) ; Armstrong & Young, Cat. Carb. Foss. W. Scotland, 

 Trans. Geol. Soc. Glasgow, iii. Supp. p. 52 (without description). 



/S^?. char. Transversely oval, gibbous ; anterior side large, 

 rounded; posterior side a little narrowed, subtruncate; an 

 obtusely rounded ridge passes from the beak to the anal angle, 

 leaving between it and the dorsal margin a slightly concave 

 posterior slope ; beaks large ; umbonal region convex, promi- 

 nent ; ventral margin gently and evenly rounded ; shell thin, 

 ornamented with regular, equidistant, fine, concentric strise, 

 with a few coarser concentric lines or wrinkles. 



Ohs. Fig. 5 has scarcely so truncated a posterior end as 

 Prof. McCoy's figure ; but both specimens from which our 

 figures were taken have the fine regular concentric striee de- 

 scribed by M^Coy. The strias are equidistant and very regular, 

 and appear to be quite characteristic of the shell. In fig. 6 

 tlie obtuse diagonal ridge is more pronounced, the posterior 



* 4to, 1866, p. 20, t. 1. figs. 3.3 & 34. 



t Hall's Geol. Report of Iowa, 1858, ii. p. 717, t. 29. f. G, 



Ann. (k Mag. N. Hist. Ser. 4. Vol. xviii. 8 



