Bracuiopopa.] UPPER PALAZOZOIC MOLLUSCA. 407 
Sect. IX.—MOLLUSCA OF UPPER PALASOZOIC ROCKS (Carboniferous and Permian). 
3rd Sub-kingdom. MOLLUSCA. See page 185. 
2nd Class) PALLIOBRANCHIATA. See page 185. 
2nd Ord. Bracnutopopa. See page 186. 
2nd Family. ORBICULIDA. See page 188. 
Genus. DISCINA (Lam.). See page 190. 
DiscinA BULLA (M/°Coy). Pl. 3. D. fig. 82. 
Ref—Ann. Nat. Hist. 2nd Series, Vol. X. 
Dese.—Hemispheroidal, regularly tumid, inflated; base circular; antero-posterior profile nearly semi- 
circular; greatest depth not at the apex, but at about the middle of the length. Surface glossy, smooth, or with 
very faint, obsolete, obtuse, concentric, and longitudinal striz; a small sulcus extends anteriorly a short way 
from the apex, which is obtuse, and nearly vertically over the posterior margin. Length seven and half lines, 
width the same, proportional depth +, distance of apex from posterior margin = 
The remarkably inflated bubble-like form of this species easily separates it from any I know. The beak 
is very little within the margin. The traces of concentric markings are rather broad and very obtuse lines, 
scarcely recognisable in the only specimen which has occurred; the traces of very fine longitudinal strize are 
only to be seen on one devorticated spot with a lens, the general aspect of the specimen being remarkably 
smooth. 
Position and Locality——Reddish sandy bed of carboniferous limestone at Lowick, Northumberland. 
Explanation of Figures.—P1. 3. D. fig. 32, profile, natural size; 32a, do. same specimen seen from above 
Disctina niTIDA (Phill. Sp.) 
Ref. and Syn. = Orbicula nitida Phill. Geol. York. Vol. II. t. 11. fig. 10 to 12+ O. cincta Portk. Geol. 
Rep. t. 32. f. 15. 
Desc.—Broad-ovate, posterior end slightly narrower than the anterior; free valve conoidal ; sides slightly 
compressed; greatest depth at or a little in front of apex, which is obtusely pointed, and marked with a very fine 
sulcus, about a line in length; flat valve with the fissure extending from a little behind the centre two-thirds 
of the distance to the posterior edge; margins of the fissure tumid; both valves very glossy, marked with small, 
' irregular, concentric wrinkles, and intervening very fine strie; traces in parts of very fine longitudinal striz 
[Fasc. 111.] 
