Bracuiopopa. | UPPER PALAZOZOIC MOLLUSCA. 429 
ing valve, and very deep, wide, defined mesial hollow, extending to the beak in the receiving valve ; cardinal area 
wide, triangular, curved ; foramen very large, twice as wide as high ; beaks remote. Width of average specimen 
two inches, proportional length of receiving valve ;, of entering valve 3, width of hinge-line *, height of 
eardinal area ;3, width of sinus in front margin =, depth =, depth of entering valve 3, depth of receiving 
valve *. 
In other less exaggerated specimens, the sinus in the front margin becomes gradually wider and lower, and 
the corresponding ridge and sinus less distinctly marked, approaching the var. glabra or var. oblata. In other 
specimens, too, the cardinal area becomes narrow, and the beaks more approximate; but on the whole, the variety 
is tolerably constant and strongly marked. 
On occasional specimens of all the varieties traces of the obtuse, obscure, longitudinal ridging may be seen, 
sometimes at the margin of large specimens, but sometimes on young ones at five lines from the beak ; some- 
times a finer, flat, obsolete ridging (about five in one line) seen on portions of small specimens, from the 
corresponding parts of which it is absent. The shell is rather thin and the internal casts smooth. 
Position and Locality—tThe three varieties very common in the grey carboniferous limestone of Derby- 
shire; var. oblata and var. obtusa not uncommon in the lower carboniferous limestone of Kendal; var. oblata 
very common in the lower dark carboniferous limestone of the Isle of Man. 
SprriFERA (Martinia) tmpricata (Sow. Sp.) 
Ref. and Syn. = Terebratula imbricata Sow. Min. Con. t. 384. f. 3, 4. 
Desc.—Transversely very broad-oval or suborbicular, moderately convex ; hinge-line half the width of the 
shell; cardinal area obscurely defined, triangular; beaks approximate, sides broadly rounded, front convex, 
lateral edges horizontal, middle of the front usually slightly raised into a wide shallow sinus; entering valve 
evenly and gently convex, greatest depth at about one-fourth from the beak, which is tumid and prominent ; 
no trace of mesial ridge; receiving valve moderately gibbous, greatest depth at one-third from the beak; a very 
shallow, faintly marked, mesial hollow usually extends from the beak to the front margin; cardinal area low, 
beak rather large, much incurved over it; surface of both valves marked with faint, broad, obtuse, radiating 
striz, (three to five in two lines at eight lines from the beak), interrupted by strong, subequal, broad, flattened, 
thick, concentric ridges ; three to five in three lines at six lines from the beak, the anterior edges of which they 
render obscurely nodular ; shell tissue under the lens very coarsely and irregularly fibrous. Average width one 
inch two lines, proportional length of receiving valve varying from 4 to nearly ;;;, length of hinge-line 4, height 
of area about ;;, depth of entering valve 5 to 4, depth of receiving valve = to =. 
This species is very easily distinguished from the J/. Zineata, with which some continental authors unite it, 
by the great width and coarseness of the concentric lamellar ridges, and the much fewer, broad, obtuse, longi- 
tudinal fimbriations in a given space ; it is also less wide, has generally some trace of mesial hollow, and has an 
unusually coarse fibrous tissue under the lens. 
Position and Locality—Common in the lower carboniferous limestone of Kendal, Westmoreland ; rare in 
the lower carboniferous limestone of Derbyshire; rare in the lower carboniferous limestone of Malham Moor. 
SPIRIFERA (Martinia) tinEaTA (Mart. Sp.) 
Ref. and Syn. = Anomites lineatus Martin, Pet. Derb. t. 36. f. 3. = Terebratula lineata Sow. Min. Con. 
t. 334. f. 1, 2. = Spirifera lineata Phill. Geol. York. p. 219. 
Desc.—Transversely oval, moderately convex ; hinge-line half the width of the shell (or in the long varieties 
a little more); beaks approximate; cardinal angles and sides semielliptically rounded ; front widely arched, no 
sinus in front; lateral and front margins in one plane. Entering valve gently and evenly convex, becoming 
gradually flattened towards the edges, which are acute; beak tumid, prominent, greatest depth at one-fourth 
from the beak, no trace of mesial fold: receiving valye moderately and evenly gibbous, greatest at one half from 
