470 BRITISH PALAXOZOIC FOSSILS. [ Bracuiopopa. 
side margins subparallel, front margin wide, with a shallow, rounded sinus in the middle, from which a wide, 
undefined mesial hollow extends to within an inch of the beak, which is of moderate size and curvature ; sides 
and front in old individuals, nearly vertical, short, subcylindrical. Surface usually covered (in well-marked 
examples) with nearly regular, slightly undulating, continuous, concentric, rounded wrinkles, closely set each 
with a single row of subequal, longitudinally elliptical tubercles (spine-bases), becoming very small, or obsolete, 
on the sides and ears; in other specimens the wrinkles are less strongly marked, interrupted, and more 
undulated; the spines at the same time becoming subquincuncially scattered; tubercles not confluent in 
longitudinal rows. Entering valve, quadrate, gently concave, with a slight, broadly rounded, undefined mesial 
ridge, extending from the margin to within about nine lines of the beak ; concentric wrinkles narrow, sub- 
regular, set with quincuncially arranged oval pits, tubercles on the interior closer and more rounded than those 
90 
of the receiving valve. Average width, 2 inches 9 lines, in proportion to width, length of receiving valve 3, 
of entering valve %, width of hinge-line =, depth of receiving valve about ;;, of entering valve about 7%; 
wrinkles varying from rather less than two to nearly three in a space of two lines at about an inch from the 
beak of receiving valve. 
After great hesitation, and a careful examination of numerous specimens, I have come to the conclusion 
that the P. pywxidiformis of M. de Koninck should be united to the P. pustulosa of Phillips, so that the 
restriction hitherto of the latter name to specimens with strong, regular, uninterrupted wrinkles bearing the 
spine-bases, has led to the difficulties with regard to the true P. scabricula. Asa matter of fact, scarcely any 
two examples of P. pustulosa agree in the strength or directness of the transverse ridges : in specimens perfectly 
typical in this respect near the beak, the ridges will be often ‘found indistinct, undulated, and interrupted on 
other parts; and when this is the case the tubercles generally increase in size, and become quincuncially 
arranged. I have traced the passage from the most regularly wrinkled type (like Koninck figure, op. cit. t. 12, 
f. 4), with the spines on the summits of the transverse ridges, through those in which the spines do not coin- 
cide with the (still well marked) ridges (like his t. 16. f.9), to those in which the wrinkles gradually become 
irregular, interrupted, and nearly obsolete, as in his P. pyxidiformis (op. cit. t. 16. f. 2. and t. 12. f. 1), by the 
most imperceptible gradations. In all these varieties the isolation of the tubercles, instead of their being mere 
inflations of distinct, longitudinal strice or ridges, distinguishes the species from the true P. scabricula. There 
is considerable variety in the depth of the entering valve. By some chance M. de Koninck in his monograph 
of Productus marks in his synonyms that I have described the P. punctata for this species in my volume on 
the Carboniferous Limestone Fossils of Ireland, which is not really the case. The tubercles vary considerably in 
size in specimens otherwise similar. 
Position and Locality—Common in the dark carboniferous limestone of Kendal, Westmoreland ; carbo- 
niferous limestone of Derbyshire. 
PRoDUCTA SCABRICULA (Mart. Sp.) 
Ref. and Syn. = Anomites scabriculus Martin, Pet. Derb. t. 36. f. 5 ; = Productus id. Sow. Min. Con. t. 69. f. 1.= 
P. quincuncialis Phill. Geol. York. t. 7. f.8; P. scabricula de Koninck, Monog. Prod. t. 11. f.6@ and 6 4. 
Dese.—Rotundato-quadrate, side margins subparallel, very gibbous, with or without a wide, shallow, 
undefined mesial hollow in the receiving valve, and still slighter corresponding ridge in the entering one (not 
reaching usually within an inch of the beak, and not seen in specimens that size) slightly sinuating the margin; 
hinge-line slightly less than the width of the shell, forming large, flat, nearly rectangular ears. Receiving valve 
with a large obtuse beak, the pointed apex extending beyond the hinge-line; front flattened or concave ; sides 
when old with nearly perpendicular sides. Surface covered with thick, close, subregular, rounded, longitudinal 
strize (averaging four in two lines at six lines from the beak), swelling at irregular intervals into oval, prominent 
tubercles (from each of which a curved spine half an inch long projects towards the margin when well preserved), 
which are subquincuncially arranged without interrupting the continuity of the little ridge on which they are 
developed, on which latter when strongly marked the tubercles seem mere nodular swellings; a few irre- 
gular concentric wrinkles on the ears and sides, becoming obsolete on the front. Entering valve quadrate, flat- 
