Bracuiopopa. | UPPER PALAZOZOIC MOLLUSCA. 459 
rounded, longitudinal ridge, varying in strength and persistence in different specimens, but generally short and 
faintly marked; most of the spines have the appearance of being directed towards the beak, but some of them 
are at right angles to the surface, and the spines to which they give origin are gently arched towards the front. 
Entering valve transversely oblong, very concaye, and nearly smooth in many specimens, but in all, the spine- 
bases and short longitudinal furrows therefrom, as in the receiving valve, may be observed. Length of receiving 
valve nine lines, proportional width of front =, width of hinge-line =, depth 4, length of entering valve 4, 
depth of entering valve ;. 
Although the adpressed character of the spines, or their points seeming to be directed towards the beak, 
noticed by Martin and Sowerby, is very striking in typical Derbyshire specimens, yet even in them some few 
of the spines will be noticed to be at right angles to the surface, and others slightly inclined the contrary way, 
as the spines themselves always are, and as M. de Koninck seems to think is always the case. Old specimens 
are even more elongate, arched, and narrower in the receiving valve, than the above averaged proportions, and 
in such specimens the obsolete ribbing from the spine-bases becomes more regular and continuous. The Producta 
laxispina of Phillips is clearly the impression of the entering valve of this species, as well as his P. spinulosa 
(Sow.), which has too few and irregularly placed spine-bases to be referred to that species; such impressions 
commonly shew the spine marks more strongly than the concavity of the shell itself. 
Position and Locality.—Rare in the carboniferous limestone of Craige near Kilmarnock ; not uncommon 
in the impure carboniferous limestone of Lowick, Northumberland ; not uncommon in the middle limestone of 
Poolwash, Isle of Man. 
PRODUCTA CORRUGATA (M‘Coy). 
Ref. and Syn.—ld. id. M°Coy, Carb. Foss. Irel. t. 20. f. 13; =P. tenuistriatus M. V. K. Geol. Russ. 
t. 16. f. 6 = P. Cora de Koninck, Monog. Prod. t. 4. f. 4. (not d’Orb.) 
Dese.—Semicylindrical, very gibbous; visceral portion of receiving valve hemispherical, passing gradually 
into the front, which descends at an angle of 45°; beak tumid, broad, incurved ; hinge-line very short, incon- 
spicuous in the receiving valve; cardinal angles obtuse, giving rise to three or four very large rounded wrinkles, 
which become rapidly effaced on the tumid sides before reaching the front, across which only very faint inter- 
rupted waves of growth may be occasionally seen. Surface covered with slightly flexuous, regular, narrow, 
rounded, thread-like strize (about twelve in two lines at one inch from the beak), alternately larger and smaller 
on many parts of the surface, from the new intercalated strize remaining for the greater part of their length 
less than half the thickness of the original ones; intervening sulci deep, much narrower than the strize, except 
when the outer layer of shell is removed, when they nearly equal them in width (as in my figure) ; no spines 
nor tubercles. Average length two inches, in proportion to length greatest width (near front) ;;, width of 
hinge-line ;;- 
It is only in cases where the shell has been probably fractured during the lifetime of the animal, that the 
irregularities, mutual absorption, &e. of the strize alluded to by M. de Verneuil occur, for in ordinary cases, as 
M. de Koninck observes, the striz in this species are remarkable for their rigid regularity ; they remain about the 
same size on all parts of the surface, and do not seem eyer to bifureate. M. de Koninck, in his Monograph of 
Productus, refers this species with the P. Neffedievi of de Verneuil to the Producta Cora of @Orbigny, a rap- 
prochement which I find it impossible to agree with, as the South American shell is figured with a long hinge- 
line, acute ears, none of the very large characteristic lateral wrinkles of this species, and the surface with large 
scattered spinose tubercles, and the strize separated by furrows much wider than their own thickness, agreeing 
in general shape and this latter character of the strise with the P. Negfedievi, to which it may possibly be allied, 
although that species seems also to want the great scattered spine bases, which never occur on my species, in 
which also, even when the shell is removed, the sulci between the strice are less than the strive in width, which 
M. de Verneuil states is not the case in the P. Neffedievi. In general form this slightly resembles the 
P. hemispherica, but the front is more produced and less curved in the profile; the strive are narrower and 
more distant, and the great size of the few wrinkles on each side separate this species at a glance from all others 
