420 BRITISH PALAZOZOIC FOSSILS. [ Bracuiopopa. 
The remarkable difference in aspect produced by the length slightly exceeding the width, and the entering 
valve being gently and evenly convex in the true var. ovalis (Phill.), and the flattening of the entering valve, 
greater width, and disproportionally deep receiving valve in the var. hemispherica (M°Coy), made me always 
consider them distinct species, until very recently seeing a specimen from Malham Moor, in which all the 
characters are intermediate, I therefore now unite the species, merely indicating the two forms as varieties. 
The shortness of hinge-line and height of the area between the beaks, as well as broad, simple, mesial fold, 
distinguish it from the S. integricosta (Phill.) 
Position and Locality.—V ar. ovalis common in the carboniferous limestone of Beith, Ayrshire ; rare in the 
lower carboniferous limestone of Derbyshire; var. hemispherica, not uncommon in the dark carboniferous lime- 
stone of Isle of Man; intermediate variety in grey carboniferous limestone of Malham Moor; var. hemispherica 
not uncommon in the dark lower carboniferous limestone of Lowick, Northumberland. 
Explanation of Figures.—P\. 3 D. fig. 28, var. hemispherica, side view, natural size from the Isle of 
Man, shewing the great inequality of the valves; fig. 28 a, ditto same specimen, shewing the entering valve 
and very small hinge line and cardinal area ; fig. 28 4, ditto same specimen, front view. 
SPIRIFERA PAUCICosTATA (M°Coy). Pl. 3. D. fig. 26. 
Ref —M°Coy, Ann. Nat. Hist. 2nd Series, Vol. X. 
Dese.—Globose, or very broad-ovate; hinge-line slightly shorter than the width of the shell; cardinal 
angles slightly obtuse, sides and front moderately rounded, very obtuse from the meeting of the valves at a large 
angle, front abruptly raised into a wide semielliptical sinus. Entering valve evenly convex, sides tumid, with six 
or seven strong, rounded, obtuse simple ribs on each side ; mesial ridge broad, prominent, very strongly 
defined from the beak, having three ridges about the size of the lateral ones, each of which dichotomises 
close to the margin. Receiving valve very gibbous, semicircularly arched from the beak to middle of front 
margin; mesial sinus deep, strongly defined from the beak, having at first three, subsequently six small 
obscurely marked ribs; beak very large, incurved; cardinal area moderately wide. Width nine lines, pro- 
portional length of receiving valve +, length of entering valve ;;,, depth of both valves 4, width of mesial 
fold %, height of sinus in front margin =, width of cardinal area ;;. 
This species is most nearly allied to the S. trigonalis, from which it is distinguished by the more 
spheroidal form, the obtuse rounding of the sides, and the very small number of its lateral ribs; the dis- 
tinetly ribbed mesial ridge separates it from S. pingwis, as well as its more depressed form, and the fewer, 
and more prominent radiations. 
Position and Locality—Not very uncommon in the carboniferous limestone of Derbyshire. 
Explanation of Figures.—PI. 8. D. fig. 26, end view, natural size ; fig. 26a, ditto profile; fig. 26 4, ditto 
front view. 
SPIRIFERA PINGUIS (Sov.) 
Ref—Sow. Min. Con. t. 271. 
Desc.—Globose, cardinal area narrow, beaks very approximate ; lateral margins very obtuse, the edges of 
the valves meeting sometimes without angle; hinge-line less than the width of the shell; cardinal angles 
obtuse or slightly mucronate; lateral margins straight in young, sigmoidally curved in old specimens ; front 
margin abruptly raised into a very deep oblong sinus. Entering valve inflated, moderately gibbous, tumid 
quite to the margins, which are deflected in old specimens ; eight or ten thick, obtuse, convex, simple or 
occasionally bifureate ribs on each side, varying from two to three in a space of three lines at nine lines 
from the beak; the immediate vicinity of the hinge-line nearly smooth; mesial ridge very strongly defined by 
two sulci from the beak, broad, prominent, smooth, and rounded, or divided by a mesial sulcus. Receiving 
valve inflated, very gibbous on the sides, which are nearly vertical; semicircularly arched from the beak to 
the middle of front margin; depth greatest in the middle of the length; mesial hollow very deep, wide, 
concave or flattened in the middle, and strongly defined from the apex of the beak, containing three or five 
