Bracuiopopa. | UPPER PALAZOZOIC MOLLUSCA. 475 
posterior end of the larger valve more pointed, the sides gradually converging at an angle of about 84°, the beak 
being terminal; greatest width about the middle ; middle portion of both valves evenly convex, most so at one- 
third the length from the beak, from whence the surface slopes gradually to the front and more rapidly to the 
compressed lateral margins; shell very thin, marked with very fine, inconspicuous, irregular, concentric lines of 
growth, and traces of radiating, extremely minute, fibrous striae. Average length four lines, proportional 
greatest width =, depth of one valve about +. 
This species is very closely allied to the LZ. mytiloides of Sowerby, but is generally a smaller and more 
delicate species, and is perhaps rather wider at the posterior end. 
Position and Locality—Occurs in great numbers on the surface of the Permian marl-slate at Thris- 
lington gap. 
LineuLa EvLIPTica (Phill.) 
Ref. =1d. id. Phill. Geol. York, Vol. II. t. 11. f. 15. 
Desc.—Elongate ; large valve elliptical, small valve regularly ovate ; greatest width at about one-third the 
length from the beak, from whence the margins are semielliptically rounded in the small valve, and elliptically 
pointed in the long valve at an angle of about 85°, but without distinct straightening or definition of the pos- 
terior lateral margins, which curve imperceptibly into the sides ; from the widest point both valves are regularly 
elliptically attenuated to the middle of the front, which is rather narrow and very convex; middle third of the 
valves convex from the beak to the front margin, the sides sloping rather abruptly to the lateral margins; a 
small sulcus usually in the apex of the beak. Surface with a few concentric waves of growth, and numerous, very 
fine, sharp, irregular, concentric strize under the lens, crossed by much finer, microscopic, close, radiating strize 
in certain states of preservation; short valve flatter than the long one. Average length three and half lines, 
proportional width = to =, depth about 3. 
The more lengthened, narrow, elliptical form of this small species, and its less proportional width and 
narrow front, distinguish it from the Z. mytiloides (Sow.), in which the proportional width is about 7. 
Position and Locality—Not uncommon in the black carboniferous limestone of Derbyshire. 
LINGULA LATIOR (M°Coy). Pl. 3. D. fig. 33. 
Ref. = Id. id. M°Coy, Ann. Nat. Hist. 2.S. Vol. X. 
Dese.—Broad-ovate anteriorly, gray acuminated posteriorly ; moderately convex towards the beak, 
very gradually flattened towardsgthe margifs ; sides meeting at the beak at an angle of about 75°; front wide, 
semielliptically rounded; greatest width at about the middle of the length, from whence the posterior end is 
rapidly narrowed to the beak. Surface with fine, sharply defined, strong, close, elevated, obtuse, concentric strize, 
slightly irregular from occasional branchings and interruptions; crossed in parts by longitudinal microscopic 
strie. Length four and half lines, proportional width =. 
Distinguished from the other described carboniferous Lingulw by the very wide ovate form of its anterior 
end, and the great comparativ@length and straightness of the posterior lateral edges, which by their convergence 
at so small an angle give the remarkable posterior attenuation or pointed beak characteristic of the species. In 
general appearance and surface it closely resembles some of the Russian Ungulites. 
Position and Locality.—Not very uncommon in the black limestone over the main limestone of Derbyshire, 
Explanation of Figures —P1. 3. D. fig. 33. Natural size. 
LINGULA SQUAMIFORMIS (Phill.) 
Ref. =1d. id. Geol. York, Vol. II. t. J1. f. 14. 
Desc.—Longitudinally oblong ; sides nearly straight, subparallel; greatest width near the anterior end, 
which is subtruncate, with the lateral angles obtusely rounded ; posterior end wide, rounded in the short valve ; 
posterior lateral margins short, straight, and meeting at 110° to form the short beak of the long valve; valves 
