AT 4 BRITISH PALAZOZOIC FOSSILS. [Bracutoropa. 
wide, the posterior end being pointed and without hinge-line. The opposite extreme of form is not uncommon in 
the Isle of Man, where specimens occur two or three inches long and two wide, with a depth of nearly an inch, and 
with an obtuse-angled hinge-line; and between these extremes all the intermediate forms may be noticed. Under 
all these varieties, the species is easily recognised by the extreme irregularity of its growth, as in Hinnites, there 
being nothing of symmetry between the marginal irregularities of the two sides, nor any regularity in the 
corresponding depressions, and obscurely concentric undulations of growth, which seem to produce or greatly 
increase the flexures of the striee. The great irregularity of growth distinguishes the most nearly allied varieties 
from P. hemisphwrica, and the same character and want of spines separate it from the yar. Scotica of the 
P. gigantea, to which some unusual varieties approach. 
Position and Locality—Common in the lower carboniferous limestone of Derbyshire; in the dark middle 
carboniferous limestone of Isle of Man;? rare in the dark carboniferous limestone of Lowick, Northumberland. 
Propucta TorTILIS (J7/°Coy). 
Ref. and Syn. =1d. id. M°Coy, Syn. Carb. Foss, Irel. t. 20. f. 14.=P. undatus (Defr.) de Kon. Anim. Foss. 
Bel. t. 12. f. 2.=P. undatus (Defr.) M. V. K. Geol. Russ. t. 15. f. 15,? (not of Defrance). 
Desc.—Very broad-oyate ; receiving valve rounded, gibbous, with a large, prominent, moderately incurved 
beak, extending very little beyond the hinge-line ; hinge-line rather less than the width of the shell, forming 
short, flattened, obtuse ears. Entire surface covered with broad, irregular, undulating, concentric, subangular 
ridges, having their scarp or narrow steep side towards the beak, either uninterruptedly continuous from one ear 
to the other, or short and irregularly interrupted in their passage across the middle, giving a largely crumpled 
appearance to the shell; ridges crossed by sharply defined, narrow, rounded, thread-like strize, separated by very 
narrow sulci, very regular in size (twelve to fourteen in two lines at six lines from the beak), except where 
small spine-bases occur, immediately before each of which one of the strize swells to the width of two, and from 
the base of the spine such strize being split into two or three nearly or quite as large as the adjoining ones; 
intercalated short strize assuming almost immediately the thickness of the primary ones; spine-bases small, very 
variable in number, sometimes tolerably numerous, and subquincuncially arranged, but more often nearly absent. 
Entering valve exactly resembling the receiving one, except in its less depth. Average width eleven lines, pro- 
portional length =, depth of receiving valve =, depth of entering valve 4. 
This species is easily distinguished from all others of the carboniferous period by having the whole surface 
crumpled with large, undulating, irregularly angular folds, the short steep side of which is directed towards the 
beak. I originally figured and described this fossil from the mountain-limestone under the above name, but 
almost at the same date M. de Koninck, and shortly after, MM. Murchison, de Verneuil, and Keyserling 
figured it as the Productus undatus of Defrance, stating that they supposed his principal locality (Chimay) to be 
erroneous, as it contained only Devonian strata. The more I consider M. Defrance’s description, however, the 
more strongly inclined I am to suppose he meant to indicate the really Devonian P. caperata of modern writers, 
which not only agrees with his gisement, but with his description of form of concentric wrinkles and léger 
strize ; which latter term could never haye been applied to the remarkably harsh, strong, thread-like strice of the 
present species of the carboniferous rocks, to which I therefore restore my old name. 
Position and Locality —Not very uncommon in the lower carboniferous limestone of Lowick, Northumber- 
land; middle carboniferous limestone of Poolwash, Isle of Man; rare in the black upper beds of carboniferous 
limestone, Derbyshire. 
Genus. LINGULA (See page 250). 
LINGULA CREDNERI (C‘einitz). 
Ref. and Syn, = 1d. id. Geinitz Versteinerungen, t. 3. f. 23, 24; King, Perm. Foss. t. 6. f. 25 to 27. 
Desc.—Longitudinally oblong, elliptical ; side margins very slightly convex in the middle, slightly narrowed 
and elliptically rounded at the anterior end, posterior end of small yalve broad, subtruncate, the angles rounded, 
