Bracuioropa. | UPPER PALALOZOIC MOLLUSCA. 465 
to once the length of those impressions. The regularity of the striee, even, hemispherical form, and want 
of the numerous thick, scattered, spine tubercles, separate this species externally from all the varieties of the 
P. gigantea (Sow.) ; the less gibbous form, more obtuse and closer strize (which are also more equal from 
the greater rapidity with which the intercalated striz arrive at the thickness of the others), and want of the 
great lateral wrinkles, separate it from the P. corrugata (M°Coy). 
Position and Locality —Common in the earboniferous limestone of Kendal ; lower carboniferous limestone 
of Derbyshire ; carboniferous limestone near Chepstow, Gloucestershire; in the dark lower earboniferous lime- 
stone of Ronalds-way, Isle of Man. 
PropUCTA HORRIDA (Soi.) 
Ref. and Syn.=Gryphites aculeatus Schlot. Taschenb. t. 4. f. 1. and 2, (not Prod. aculeatus Sow.) = (Prod. 
horrida Sow. Min. Con. t. 319. f. 1. +P. calva id. id. t. 560. f, 2. to 6.) = P. Hoppei Konig, Ieon. Foss. 
t. 9. f. 108. =P. tubuliferus Deshayes = P. horridus (Sow.) King, Perm. Foss. t. 10. f. 29. to 31. and 
tall tol tons: 
Desc.—Quadrate, hinge-line as long as the shell is wide, forming large, obtusely rounded, slightly convoluted 
ears in the adult (but small rectangular ones in the young). Receiving valve extremely gibbous, with a deep, 
wide, rounded, mesial furrow, commencing near the apex of the beak, and extending to the front margin ; 
profile almost semicircularly arched, but the curve of the visceral portion smaller and more abrupt than that of 
the front ; beak small and only slightly projecting beyond the hinge-line ; sides very steep, or nearly vertical in 
some specimens; one or two rows of large cylindrical spines running nearly parallel with the hinge-line on each 
side, the rest of the valve either without spines or with a few large scattered ones, or more rarely having 
obscurely longitudinal rows of eight to ten rather smaller ones, those nearest the margin always largest. Surface 
crossed by rather strong, irregular, imbricating lines of growth, and either even or obscurely and irregularly 
ridged longitudinally. Entering valve also with one or very rarely two long cylindrical rows of spines, projecting 
externally like those of the receiving valve; convex externally near the ears, and obtusely rounded longitu- 
dinally, mesial furrow and the intervening spaces on each side only moderately concave, leaving a very deep space 
between the valves for the animal. Average width one inch seven lines, proportional length of receiving valve 
, of entering valve 4, depth of receiving valve =, depth of entering valve =. 
Some specimens of this species are considerably higher, narrower, and more parallel-sided than others ; and 
though some authorities believe those varieties characteristic of separate localities, I have found them together 
in the limestone of Humbleton. Some varieties are nearly free of large spines on the body of the shell, forming 
the P. Calva of Sowerby, while others identical have them in all the varieties noted above. The internal casts 
of the receiving valve have the muscular impressions in the cavity of the beak, apparently very prominent, from 
the great depth of the sulcus between them, of a longitudinally ovate form, and about half their width apart. 
Casts of the entering valve shew the large bifid rostral tooth, from which the septum extends two-thirds the 
Jength of the shell; the dendritic and smooth reniform impressions, nearly resembling those of P. semireticulata, 
the surface beyond which is closely marked with small spinulose points. Prof. King has given a valuable series 
of figures in his Memoir on the English Permian fossils, shewing both the external and internal characters very 
perfectly. He also notices that the layer of shell beneath the outer transversely striated one is composed of 
coarse longitudinal fibres. Prof. King suggests that this species may be found in the carboniferous rocks of 
Fermanagh; but though I have examined probably hundreds of Productz from that neighbourhood, I have 
never seen a trace of it. 
Position and Locality—Very common in the Permian magnesian limestone of Humbleton. 
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