A98 BRITISH PALAXOZOIC FOSSILS. [Lame iiprancurata- 
the whole length of the hinge-line a little below the simple erect dorsal margins; traces of two minute cardinal 
teeth under the beak of each valve ; surface with from three to six strong, subequal, narrow ridges, radiating 
from the beak over the posterior half of the shell; the ridges rather less than half a line wide, and nearly a line 
apart at the margin; the anterior portion of the shell destitute of radiating ridges, but all the surface covered 
with very minute concentric plice of growth. Average length one inch one line, proportional width (greatest 
about the middle of the length) 4, length of anterior end 5, depth of both valves 7%. 
I have purposely omitted referring to King’s figures of the short unridged variety, which seems distinct ; 
I might remark that the specimens I have examined shew only the most minute traces of the cardinal teeth, 
represented so strongly in Professor King’s figures. The near parallelism of the dorsal and ventral margins, 
and want of byssal sinus in the latter, separate this fossil from the ridged varieties of Mytilus Pallasi de 
Verneuil. 
Position and Locality—Not uncommon in the Permian limestone of Humbleton. 
Genus. PINNA (Linn.) 
Gen. Char.—Shell very long, triangular, equivalve; beaks pointed, terminal; posterior end very broad, 
truncate, widely gaping; one large, subtrigonal, posterior muscular impression, and one very small reniform one 
at the beaks; cartilage very long, narrow, internal, supported by a very slender ridge close within the cardinal 
edges; no teeth; shell of one internal laminated layer, and an external vertically fibrous layer. Animal long, 
mantle quite open, with ciliated edges; mouth with two foliaceous lips and two pairs of short palpi, united in 
part of their length; foot narrow, conical, with a large silky byssus at its base. 
Differs from Mytilus by the fibrous texture, the gaping of the posterior end of the shell, and the absence 
of any siphons to the animal. 
The recent species abound most in temperate and warm seas, fixed by their byssus, with the beak down- 
wards, to foreign bodies, or sunk in the sand with only their truncated end exposed, a little below low-water 
mark, (D’Orb.) 
PINNA FLABELLIFORMIS (J/artin). 
Ref. and Syn. = Conch. Pinnites flabelliformis Martin, Pet. Derb. t. 6.=C. P. nudus id. in the Syst. 
Arrangement ;? = Pinna costata Phill. Geol. York. Vol. II. t. 6. f. 2. 
Desc.—V alves elongate, triangular, nearly three times longer than wide; sides covered in their whole width 
by wide, nearly straight, rounded, or slightly flattened ridges, of irregular, unequal size (varying, at six inches 
from the beak, from half a line to two lines, but more commonly a line and half, wide), separated by deep, con- 
cave sulci, varying from little less than the width of the ridges to one-third of that width irregularly ; section 
obscurely rhomboidal near the beaks, the valves becoming more flattened towards the posterior end; surface 
crossed by close, obtuse, obscure lines of growth, the ridges rendered very slightly flexuous by occasional sub- 
tubular rugosities, scattered at wide intervals over the ridges and furrows; within an inch from the beak the 
radiating ridges become obsolete. Average length eight inches, proportional width about =. 
This species not unfrequently exceeds a foot in length; some of the ridges, particularly those near the 
hinge-line, remain simple throughout, while others dichotomise irregularly, the pair thus produced being recog- 
nisable to the end by the much narrower and shallower divisional sulcus. The small, subtubular, nodosities are 
very rarely to be seen, they break off so readily in the matrix. The depth near the beaks considerably exceeds 
the width, and at three inches from the beaks the ridges are so reduced in size as only to measure six in the 
space of half an inch. 
Position and Locality—Not uncommon in the carboniferous limestone of Derbyshire; not uncommon in 
the dark lower carboniferous limestone of Poolwash, Isle of Man; in dark earthy carboniferous limestone of 
Craige near Kilmarnock. 
