984 BRITISH PALALOZOIC FOSSILS. [ LaAmMELLIBRANCHIATA, 
before the beaks to the posterior margin of the anterior adductor, forming a deep slit in the casts. Surface 
generally smooth, or nearly so. 
These Paleozoic shells have been confounded with Nucula (Sow. Phil. &c.), from which they differ in 
the absence of the ligamentary pit in the hinge, and in the anterior internal septum; they have also been con- 
founded with Cucullea, from which they differ in wanting the hood-like plate of the posterior adductor, and 
having the septum in the anterior end; and with Clidophorus (Geol. Surv. of Great Britain), from which they 
differ in having the hinge crenulated as in Arca. 
CUCULLELLA ANTIQUA (Sow. Sp.) 
Syn. = Cucullea antiqua Sow. Sil. Syst. t. 3. f. 16 and 12a = Arca sub-antiqua W@Orb. Prod. 
Sp. Ch.—Subquadrate, moderately convex; ventral margin slightly convex, subparallel with the hinge-line ; 
anterior end rather large, rounded ; clavicular ridge thick, slightly oblique, reaching rather less than half-way 
from the beak to ventral margin; numerous minute, slightly oblique teeth on the hinge-line; posterior end 
subtruneate, oblique; average length three and half lines; in proportion to length, greatest width (from beak to 
opposite ventral margin) =, depth of one valve about ;;, length of anterior end about =, of clavicular ridge 
the same, from beak to end of hinge-line =. 
I have not yet seen good specimens of this species, which is distinguished from the C. ovata by its smaller 
size, more quadrate form, longer hinge-line, and consequently wider posterior end ; the clavicular ridge is also 
considerably shorter and thicker. 
Position and Locality.—Tilestone of Storm Hill, Llandeilo, Caermarthenshire, and schists of Conway 
Falls. 
CUCULLELLA COARCTATA (Phill. Sp.) 
Ref. and Syn. = Nucula coarctata Phil. Mem. G. Surv. t. 22. f. 1 to 4. 
Sp. Ch.—Ovate, broadly rounded in front, gradually narrowing posteriorly, gibbous towards the beak, 
most so rather more than one-third from the anterior end, becoming gradually compressed posteriorly: beak 
small, prominent ; anterior end elliptically rounded ; anal angle scarcely defined ; posterior margin very obliquely 
rounded ; respiratory angle narrow, rounded, with a small sinus between it and the gently convex ventral margin, 
from which a shallow impressed furrow extends nearly to the beak; teeth large, clavicular ridge slightly oblique, 
extending more than half way from the beak to the margin; length six lines ; im proportion to length, greatest 
width (from beak to opposite ventral margin) +, length of anterior side 34, length of clavicular ridge ;;,, from 
beak to end of hinge-line 4; depth of one valve =; surface with extremely minute concentric lines, crossed by 
traces of longitudinal microscopic striz. 
Position and Locality—Common in the Upper Ludlow rock of Benson Knot, Kendal, Westmoreland ; 
also in the schists of Dinas Bran, Llangollen, Denbighshire. 
CUCULLELLA OVATA (Sow. Sp.) 
Syn. = Cuculleea ovata Sow. Sil. Syst. t. 3. f. 126= Arca subovata @Orb. Prod. 
Sp. Ch.—Regularly ovate, evenly gibbous; beaks obtuse, anterior end broadly rounded; ventral margin 
gently convex ; posterior end narrow, elliptically rounded at the respiratory angle; cardinal angle very obtuse ; 
hinge-line with numerous, very minute, transverse teeth ; clavicular ridge extending perpendicularly, slightly 
more than half way from the beak to the ventral margin; surface crossed by minute concentric lines of growth ; 
average length eleven lines; in proportion to length, greatest width (from beak to opposite ventral margin) =, 
20 46 
length of anterior end *, from beak to end of hinge-line 4, greatest depth of one valve =, length of clavicular 
ridge =. 
Position and Locality.—Common in the Upper Ludlow rock of Brigsteer, and Benson Knot, Kendal, 
Westmoreland ; the similar micaceous greenish beds of Llechclawdd near Llandovery, S. Wales; tilestone of 
Horeb Chapel, Llandovery, S. Wales; and Storm Hill, Llandeilo; Upper Ludlow rock of Derby Arms, 
near Kendal, Westmoreland. 
