250 BRITISH PALAZOZOIC FOSSILS. [Bracniopopa. 
valve gently concave; receiving valve depressed, convex in the middle, considerably more arched than the entering 
valve, flattened at the ears, sometimes with a slight narrow mesial longitudinal sulcus, rather abruptly arched 
downwards at the margins, greatest depth about the middle of the length; beak very small, not projecting : 
surface of both valves radiated with very numerous coarse, rugged, strize, separated by sulci half their width ; 
striee branching once or twice at one or two lines from the beak; when decorticated, the intervening sulci 
marked with coarse punctures; about twenty strize in two lines, at two lines from the beak ; usually two or three 
strong concentric imbrications of growth, and about four long, slender spines projecting from the hinge-line on 
each side of the beak, diverging obliquely outwards and backwards; interior marked with strong longitudinal 
lines of coarse punctures ; with three thick, short, subequal ridges from the beak, one central, the others diverging 
at 100°. Width eight lines, proportional length =, depth of receiving valve 5. 
The strize are rather thicker at a line and half from the beak (before their first branching) than at any other 
part of the shell. In some old specimens the margins are faintly and irregularly undulated radiatingly. 
Position and Locality——Very common in the Upper Ludlow rock of Woolhope; very common in the 
Upper Ludlow rock, and limestone, of Mortimer’s Cross, Aymestry, Herefordshire ; schists of Cwm Craig ddu, 
Builth, Brecknockshire ; Upper Ludlow limestone and mudstone near Ludlow, Shropshire; green quartzose 
Upper Ludlow of Benson Knot, Kendal, Westmoreland; Upper Ludlow rock of Downton Castle, Aymestry, 
Herefordshire ; limestone of Kington, Herefordshire; Upper Ludlow micaceous quartzite of Lamb-rigg Fell, 
N. end of Potter’s Fell, and limestone of Underbarrow, Kendal, Westmoreland ; ? sandy schists of Middleton 
Park, Llandeilo, Caermarthenshire ; Upper Ludlow rock of Burton and Brockton, near Wenlock. 
11th Family. LINGULIDZ (D’Or?.) . 
Arms free, fleshy, inrolled, without shelly supports from the valves, capable of being entirely protruded 
beyond the shell, provided with long, firm fimbrize; valves unconnected by a hinge; pedicle of attachment 
passing out between the beaks of the two valves, neither of which are notched or perforated. Shell corneous, 
dense, fibrous, subequivalve, equilateral. There is a heart-like vessel on each side, about one-third the length 
from the beak, giving off one large trunk on each side; the subdivisions of the branchial vessels give off vascular 
loops, arranged as separate lobes of the mantle, resembling the gills of the higher J/ol/usca, and subservient to 
respiration ; close to the beak are the conjoined impressions in each valve of the posterior pair of muscles; at 
about one-third the length of the shell in front of them are two small ovate, approximate ovaries, exterior to 
which are the large impressions of the decussating muscles which produce the sliding motion of the valves on 
each other. Just in front of the ovaries are two very large oval lobes of the liver, a third lobe of which is 
placed in the median line immediately in front of the posterior pair, and is flanked on each side by a rather 
small, oblique, ovate impression of the anterior pair of adductor muscles in each valve ; considerably in front of 
these, in the median line, are the conjoined, triangular impressions of the anterior pair of muscles, which extend 
‘into the pedicle at the posterior end. 
The Family contains Three Genera.—Ist, Lingula ; 2nd, Obolus ; 3rd, Spondylobolus. 
Genus. LINGULA (Brug.) 
Gen. Char.—Subequivalve, equilateral, longitudinally ovate or subpentagonal, both valves channeled equally 
at the beaks, for the passage of the pedicle (one beak a little longer and more pointed than the other, which 
latter has a narrow internal flat area) ; internally each valve has a thickened pad in the middle, and the shorter 
one has in front of it a prominent internal septum. 
The species of this genus grow wider proportionally with age. 
Professor Phillips mentions (Mem. Geol. Surv. Vol. II. Pt. 1. p. 370) that he is induced to propose a new 
genus, Glossina, for such Lingulw as were not really equivalye; but no species of the genus either recent or 
fossil have the beaks really of equal length. 
