LaMELLIBRANCHIATA, | LOWER PALAOZOIC MOLLUSGA. 985 
5th Family. NUCULID. 
Shell equivalve, regular, closed all round, without external ligamentary facets between the beaks ; hinge of 
very numerous small teeth; ligament internal or external, placed in a distinct pit under the beaks; pallial 
impression entire; two adductors; surface usually covered with periostraca. Animal large; mantle entirely 
open ; foot very large, compressed, slit beneath, capable of dilatation at the end; gills forming fringes of free 
filaments. 
Differ from the Arcide by the want of the ligamentary facets beneath the beaks, and having the cartilage 
in a separate internal pit. 
Genera :—Ist, Nucula; 2nd, Nuculina; 3rd, Limopsis (= Pectunculina). 
Genus. NUCULA (Lam.) (- Leda). 
Gen. Char.—Oval or oblong, inequilateral, equivalve ; cartilage internal, placed in a pit under the beak; 
teeth very long. 
Distinguished from Pectunculus by the absence of ligamentary facets, the angulated hinge, and oblique 
cartilage-pit. 
Nucuta Anexica (d Orb.) 
Syn. = N. ovalis Sow. Sil. Syst. t. 5. f. 8 (not of Zieten). 
Sp. Ch.—Ovate ; beaks large, obtuse, very prominent ; anterior side short, widely rounded ; ventral margin 
slightly convex ; posterior end obliquely subtruncate, narrow; valves very gibbous near the beak, becoming 
rapidly compressed towards the ventral margin and posterior end; posterior slope very steep, defined by an 
obtuse ridge; in the casts the adductor impressions very strong, posterior adductor surmounted by a minute 
accessory impression, two or three small accessory impressions in the cavity of the beak; hinge-teeth large, 
long, eight or nine behind the beak, and seven or eight in front; cartilage-pit beneath the beaks large; surface 
apparently smooth or with fine concentric lines of growth; length five and half lines ; in proportion to length, 
greatest width (from beak to opposite margin) 4, length of anterior end %, depth of both valves =. 
This is the first instance among Pal:eozoic fossils in which I haye seen the cartilage-pit between the beaks 
interrupting the row of hinge-teeth, in the manner of the true Nucule. 
Position and Locality—Common at Long Sleddale, Westmoreland, and in the Upper Ludlow rock of 
High Thorns, Underbarrow, and Brigsteer, Kendal, Westmoreland. 
Nucuta LEVATA (fail). Pl. 1. K. fig. 4 and 5. 
Ref.—Pal. N. York, t. 34. f. 1. 
Sp. Ch.—Obliquely ovato-rhomboidal, a little longer than wide, very gibbous near the beaks, becoming 
rapidly compressed towards the margins; steep posterior slope undefined ; beaks large, very prominent a little 
on the anterior side of the middle; anterior end broadly rounded; posterior end narrow, obliquely truncate ; 
surface marked with small concentric, close ridges; teeth rather large, hinge-line obtusely angulated beneath 
the beaks, where a small cartilage-pit separates the anterior from the posterior teeth, six or seven behind the 
beaks ; adductor impressions moderately strong, a small accessory impression over the posterior one ; length (of 
short variety) four and half lines ; in proportion to length, greatest width (from beak to opposite margin) nearly 
the same, depth of both valves =, length of anterior side ;j;,, width of posterior end >. 
The much greater height in proportion to length, and larger and more prominent beaks, separate this 
species constantly (though liable to some variation) from the V. Anglica (d’Orb.), and in a still greater 
degree from the WV. /wvis (Sow.), to which Hall supposes it analogous. 
Position and Locality—Common in the schists of Dinas Bran, Llangollen, Denbighshire ; abundant in 
the schists of Milltit Cerrig, Llangynnog, Montgomeryshire: in the schists of Plas Madoe, N. of Llanrwst : 
and extremely abundant in the schists of Conway Falls (the American localities are from the middle of the 
Trenton limestone, and also the Hudson river group). 
