466 BRITISH PALAZOZOIC FOSSILS. [ Bracuiopopa. 
PropuctA KEYSERLINGIANA (de Kon.) 
Ref—ld, id. de Koninck, Monog. Prod. t. 14. f. 6. 
Desc.—-Rotundato-quadrate, transverse, depressed. Receiving valve with the beak narrow, very prominent, 
visceral portion gently gibbous, rather abruptly arched to the short front, so that the profile, though nearly 
semicircular, is slightly flattened and elongate towards the produced beak ; ears moderately large, nearly rect- 
angular, rather strongly defined at the sides of the beak, but gradually blending with the body of the shell 
towards the margin; middle of the front with a slight mesial depression ; whole of the visceral portion rugged, 
with very small, round, irregular concentric wrinkles, bearing thickly crowded, very large, obtuse, spine tubercles, 
rounded on all the posterior portion, becoming elongate near where the abrupt arching of the front begins, and 
diminishing in size and prominence on the narrow front, where also the concentric wrinkles give place to fine 
concentric strive of growth. Entering valve flattened, very slightly concave in the middle, flattened on the ears, 
strongly marked with the concentric wrinkles and rounded pits, representing the tubercles of the opposite 
87 80 
valve. Average width six lines, length of receiving valve {j,, length of entering valve =, depth of receiving 
valve , depth of entering valve ;;. 
The concentrically and minutely wrinkled visceral portion, with the very large crowded spine tubercles, 
abruptly becoming smaller or almost obsolete at the edge, as well as the small size and flattened entering valve, 
easily distinguish this from any other species. The wrinkles are very small and only visible between the spines, 
but they, as well as the flatness of the’ entering valve and more crowded tubercles, and less gibbous receiving 
valve, separate it from the P. aculeata; and the greater proportional width, &c. separates it from the 
P. Deshayesiana, which latter, however, I have not seen. I have compared the English with authentic Belgian 
specimens, to be certain of the identity. 
Position and Locality.—Rare in the carboniferous limestone of Derbyshire. 
PRODUCTA MARGARITACEA (Phill.) 
Ref. and Syn. = P. margaritacea Phill. Geol. York. t. 8. f. 8. + P. pectinoides id. id. t. 7. f. 11; ? + P. flexistria 
de Kon. Monog. Prod. t. 17. f. 1. (not of M*Coy). 
Dese.—Suborbicular, varying from longitudinal to transverse; hinge-line slightly less than the width of the 
shell, forming small, brittle, nearly rectangular ears, not strongly defined from the body of the shell. Receiving 
valve evenly gibbous, but varying greatly in depth, most gibbous in the middle, gradually sloping towards the 
sides and front margin, more abruptly arched towards the beak, which is generally large, very obtuse, and over- 
hanging the hinge-line, but varies greatly in size. Surface covered with thick, subequal, obtusely-rounded ridges 
(about four in two lines at six lines from the beak), separated by much narrower shallow sulci; the ridges 
increase in thickness from the beak for a length of seven or eight lines, after which most of them fork into two, 
the branches being equal, and divided by a smaller sulcus than that separating the primary ridges; surface 
crossed by thin, obsolete, foliaceous, imbricating strive of growth; very few or no spine-bases on the body of 
the shell, but usually one or three on each ear. Entering valve moderately and evenly concave, with the con- 
centric imbricating lines of growth more strongly marked than on the receiving valve, but the ridging often 
almost obsolete ; substance of the shell very thin, foliaceous, and often nacreous. Length of very gibbous old 
specimen one inch three lines, proportional width *, length of entering valve 7, depth of receiving valve ,j;,, 
depth of entering valve ; width of wide depressed variety, young specimen, 11 lines, proportional length of 
receiving valve (1, length of entering valve 7, depth of receiving valve ;, depth of entering valve ;;; length 
and width of receiving valve of intermediate specimen one inch three lines, length of entering valve 7, depth of 
receiving valve >. 
This species varies extremely in the relative proportions of the depth of the receiving valve, so that a 
comparison of intermediate specimens makes me now think with M. de Koninck, that the P. margaritacea 
