460 BRITISH PALAXOZOIC FOSSILS. [ Bracutopopa. 
that I know. I have not seen the entering valve, but M. de Koninck states it to be flattened and concentrically 
wrinkled in the visceral part, and to follow the receiving valve closely on the descending front. 
Position and Locality—Rare in the lower limestone of Kendal; small, more finely striated variety, with a 
few little spines, rare in the dark carboniferous limestone of Lowick, Northumberland. 
PRODUCTA COSTATA (Sow.) 
Ref.—id. Sow. Min. Con. t. 560. f. 1; id. id. M. V. K. Geol. Russ. t. 15. f. 13. 
Desc.—Semicylindrical, short, subquadrate, sides subparallel, the front a little wider at margin than at its 
junction with the visceral disk ; sides slightly convex, rapidly sloping to the thick inrolled conical ears, which 
project abruptly from them; each ear with a large, rugged, semicircular ridge set with large spines, and sepa- 
rated from the side of the shell by a nearly smooth sulcus. Receiving valve with the profile of the front gently 
convex, but abruptly arched over, nearly at right angles, to form the moderately convex visceral disk; a very 
deep, wide, obtusely angular sinus extends nearly from the beak to the front margin; whole shell with eighteen 
to twenty very thick, broad, convex, irregularly unequal, longitudinal ribs (measuring three in four lines on the 
front), some of which support a single, strong, cylindrical spine ; intervening sulci deep, concave, much narrower 
than the ribs; the longitudinal ribs smaller, more equal, and more numerous on the rostral portion (two, three, 
or four of these often coalescing to form one of the ribs of the front), where they are crossed by regular con- 
centric wrinkles, equalling them in size and distance from each other, thus producing a regular reticulate 
tuberculation, between which the transverse or the longitudinal furrows seem largest according to the direction 
of the light. Greatest width (along the hinge-line) one inch eleven lines, proportional length of front =, length 
of visceral disk %, width of front =. 
As M. de Koninck has already observed in his often-quoted Monograph of this genus, the circumstance 
that M. de Verneuil described internal casts sufficiently accounts for the differences in the proportional dif- 
ference in the ribs and sulci, as given by that excellent writer and other people. The ribs being so very large, 
and the shell being thin, gives an appearance to the internal casts nearly like that of the exterior, with the 
difference that the ribs seem much narrower, and the sulci much wider. The remarkable character of the more 
numerous ridges of the visceral disk, uniting to form the fewer and thicker ribs of the front, is generally seen 
most strongly about the middle of the specimens, where as many as three or four commonly unite to form a rib 
of the front; on either side of this set there are not more than two coalescing to form a front rib, and the 
greater number of ribs are simple from the front margin to the beak. The thick conical ears are nearly 
smooth, except the thick, rugged, spinose ridge near their base. The transverse lines of growth alluded to by 
most writers are very close, fine, and barely perceptible to the naked eye, not comparable to the transverse lines 
of Sowerby’s figure, which, together with the perfect flattening represented therein, may have been produced by 
wear. I have not seen the entering valve, but it is described as resembling the receiving one except in the 
flatness of the visceral disk, leaving as great a space between the valves as in the P. semireticulata. 
Position and Locality—Rare in the dark carboniferous limestone of Lowick, Northumberland. 
PRODUCTA ELEGANS ((/°Coy). Pl. 3. H. fig. 4. 
Ref—M°Coy, Synop. Carb. Foss. Irel. t. 18. f. 18. 
Desc.—Longitudinally ovate ; receiving valve extremely gibbous, arcuato-conical ; beak very large, rounded, 
incurved below the hinge-line ; hinge-line rather less than the width of the shell, ears very small, slightly obtuse, 
not abruptly defined. Surface with about sixteen, regular broad, subequal, transverse ridges, very obtusely 
angulated in the middle, each haying three or four rows of small, close-set, spinulose puncta on the rostral 
portion, which is considerably narrower than the anterior unpunctured portion, which forms a broad, smooth, or 
concentrically striated band between each of the narrow spinulose bands (two punctured and two smooth bands 
in a space of two lines at five lines from the beak). Entering valve very slightly and regularly concave, with 
