BracuiopopA.] UPPER PALAZOZOIC MOLLUSCA. 467 
and P. pectinoides of Phillips are but varieties of one species; and in the same way I find a shell exactly 
agreeing with de Koninck’s P. flexistria (which is not identical with my species of that name) is only an 
extreme gibbous form of the same species. The more gibbous the receiving valve, the larger and more 
incurved the beak seems to be, and the greater seems to be the space for the animal between the valves, as 
the entering valve, though also variable in depth, does not vary in so great a proportion as the receiving one. 
In perfectly typical specimens the length and breadth of the receiving valve are about equal, but the old gibbous 
specimens are generally a little longer than wide, and the depressed varieties a little wider than long. 
Position and Locality—Not uncommon in the carboniferous limestone of Derbyshire ; rare in the car- 
boniferous limestone of Kendal. 
PropucTA? MARGINALIS (de Kon.) 
Ref.—Id. id. de Kon. Monog. Prod. t. 14. f. 17. 
Dese.—Often slightly unsymmetrical ; receiving valve quadrato-hemispherical, visceral portion very gibbous 
in the middle from the arched deflection of the front, but only moderately convex towards the beak, which is 
very small and not prominent; hinge-line rather shorter than the width of the shell, forming very small, nearly 
rectangular ears, from which a strong concentric sulcus extends nearly parallel with the front margin, defining 
a slightly projecting front, about two lines long, which is ribbed by thick, rounded, longitudinal costze (about 
three in two lines), the rest of the surface being marked by fine, irregular, concentric wrinkles, and numerous 
irregularly scattered, oval, spine bases; substance of the shell very thin, leaving the exterior ornaments usually 
impressed on the cast, with the very superficial traces of the two broad, ovate, muscular impressions. Width 
nine lines, proportional depth ;;. 
The narrow, prominent, longitudinally-ribbed front margin, so different from the minutely wrinkled and 
tuberculated other parts of the shell, easily distinguishes this remarkable species. I have only seen the receiving 
valve, but according to M. de Koninck the entering valve has no longitudinally-ribbed margin, is only slightly 
concave, and shews occasional traces of rudimentary area, which would probably place the species in Stro- 
phalosia of King. 
Position and Locality—Rare in the carboniferous limestone of the Isle of Man. 
Propucta Martini (Sow.) 
Syn. and Ref. = Anomites productus Martin, Pet. Derb. t. 22. f. 1 to 3. = (Producta Martini Sow. Min. Con. 
t. 317. f. 2. + P. concinna id. id. t. 318. f. 1.) 
Dese.—Subcylindrical, very elongate, front margin slightly dilated, irregularly undulated in old specimens ; 
hinge-line less than the width of the shell, forming inconspicuous square ears, not projecting from the sides ; 
visceral portion very convex, nearly vertical, passing by a nearly semicircular curve into the vertically extended 
front, with or without a shallow, irregular, mesial hollow; nine or ten very small, slightly marked, concentric 
wrinkles on the sides, which become nearly or quite obsolete across the middle, not interrupting the thick, 
obtuse, nearly smooth, broadly waving, longitudinal striz, which are separated by very much narrower sulci 
and di- or tri-chotomise irregularly on various parts of the shell, but principally at the front margin (averaging 
five to seven in two lines at one inch from the beak); a very few small spines on the body of the shell, not wider 
than one of the strize, a small group of five or six larger ones close to the cardinal angle on each side. Entering 
valve with the visceral disk flat, with a very faint mesial furrow, or none, crossed by nine or ten small, faintly- 
marked, concentric wrinkles, not interrupting the thick, radiating strize ; margin of the visceral disk bending 
downwards, and then abruptly outwards at right angles, to touch the interior of the descending front of the 
receiving valve, with which the remaining portion of the descending front is in contact, the geniculation pro- 
ducing a flat, horizontal margin, about a line and a half wide, a little below the level of the visceral disk, and 
marked with fainter strize than the rest of the shell. Average length one inch seven lines, proportional width of 
