Bracutopopa. | UPPER PALAZOZOIC MOLLUSCA. 457 
Position and Locality —V ery abundant in a piece of the black upper carboniferous limestone of Derbyshire. 
Explanation of Figures.—P1. 3. D. fig.31. Magnified six diameters; the lower and right hand portions 
shew the external shell, and longitudinally sulcated surface, the remainder of the figure shews the close lines of 
strong punctures, and small mesial sulcus of the beak, as exhibited on internal casts; the line above shews the 
natural size. 
Subgenus. STROPHALOSIA. See page 387. 
LertmNA (Strophalosia) caAncrini (MZ. V. K. Sp.) 
Ref. and Syn.=Productus Cancrini Murchison, de Verneuil and Keyserling, Geol. Rus. p. 273. and de Koninck, 
Monog. Prod. t. 11. £. 3=Strophalosia Morrisiana King, Perm. Foss. t. 12. f. 18 to 32%= Orthothrix 
lamellosus Geinitz, Verst. t. 5. f. 16. 
Dese.—Rounded, greatest width about the middle; hinge-line rather less than the width of the shell, 
forming obtuse-angled, inconspicuous, flattened ears. Receiving valve slightly longer than wide, evenly gibbous, 
most so in the middle, without mesial sinus; varying greatly in depth, the posterior or rostral half more arched 
in the profile than the front; no mesial hollow; beak small, obtuse, strongly incurved, and slightly projecting 
beyond the hinge-line; cardinal area low, triangular ; foramen and pseudo-deltidium higher than wide. Surface 
covered with very fine, filiform, equal, occasionally interrupted strize (about twenty in two lines at six lines from 
the beak), about the same size in all parts of the shell, with very irregularly scattered spine bases, which are 
round on the sides, but form cylindrical, very prominent, longitudinal ridges, one to two lines long, and as thick 
as two or three of the striz on the middle portion of the shell. Entering valve moderately concave, leaving a 
considerable space for the animal, with a very narrow cardinal area; surface usually with strong concentric 
lines of growth, which obscure the longitudinal strize and the spine tubes, which latter are more rounded than in 
the receiving valve ; cardinal teeth and internal impressions as in the generic character. Average length one 
inch, width a little more or a little less than the length, proportional depth =. 
Professor King distinguishes his S. Morrisiana from the Russian S. Cancrini by its being wider than long, 
and more depressed, but nearly all his figures of receiving valve are longer than wide; and a specimen presented 
by him to the Cambridge collection has a greater proportional depth than one of the proportional measurements 
given for P. Cancrini in the Geology of Russia. I have little doubt therefore of the identity of the species, and_ 
would have none, but that MM. Murchison, de Verneuil, and Keyserling, seem to describe the strize as coarser 
than I observed them in the English species. 
The absence of the ears gives most specimens an ovate outline, widest in front. 
Position and Locality—Common in the Permian magnesian limestone of Humbleton Hill.—(In Russia it 
seems to abound everywhere in the lower stage of the Permian). 
LerTmNA (Strophalosia) EXCAVATA (Geinitz Sp.) 
Ref. and Syn. = Orthis excavata Geinitz, Neues Jahrbuch for 1842. t. 10. f. 12, 18 = Orthothriz id. id. 
Versteinerungen, t. 5. f. 30 and 37. t. 6. f. 20 = Strophalosia id. King, Perm. Foss, t. 12. f. 13 to 17. 
Dese.—Rounded or transversely very broad-oval, the greatest width at about the middle of the length; 
hinge-line scarcely two-thirds the width of the shell, forming scarcely perceptible ears. Receiving valve evenly 
gibbous, greatest depth rather behind the middle, rostral portion broad, tumid; beak small, scarcely passing the 
hinge-line. Entering valve deeply concave ; cardinal area of both valves together about four times wider than 
high. Surface of both valves with a few concentric lines of growth, and covered with very numerous, minute, 
tubular, spine-bases, a little more than their diameter apart, arranged subquincuncially, or sometimes in obscure 
lines, divaricatingly arched from the beak to the lateral margins (seven or eight in two lines at four lines from 
the beak). Width seven or eight lines, proportional length of receiving valve >, length of entering valve ¥,,, 
depth of receiving valve =, depth of entering valve ;;. Internal impressions as in S. Goldfusst, but the reniform 
impressions longer. 
3N2 
