184 
CONCHIFERA. 
Nucula. 
curved, and approximating; back gradually sloping from tlio 
beaks ; basal lino gently curved; surface with regular, trans¬ 
verse, shallow furrows, or lines of growth, and a few short, 
oblique, shallow ones crossing in a lozenge manner at the an¬ 
terior side. 
The Greensand, Staple Hill and Devonshire. 
20. Trigonia d.edalea.— The Handsome Trigonia, pi. 
LXXVI. fig. 21. 
T. deedalea. Parkinson, Org. Rem. III., p. 176, pi. 12 , 
fig. 6 . Sowerby, I. p. 198, pi. 88 . 
Oblong-ovate, trigonal; a longitudinal, tuberculated ridge, 
dividing the valves into nearly equal halves; both sides an¬ 
gular near their centre, the anterior ono gradually rounded 
both above and below the angle ; posterior side slightly hol¬ 
lowed beneath the beaks, and thence a little arcuated till it 
reaches the centre, below which there is a double flexure; 
beaks small and pointed ; anterior side with many scries of 
large tubercles, set in arcuated ridges; posterior side with 
a series of less regular ones running downwards from the side 
towards the central ridge. 
The Lower Greensand, Parham and Blackdown. 
21 . Trigonia incurva. —The Incurved Trigonia, pi. 
LXXVI. fig. 42. 
T. incurva . Sowerby, Geo. Tr. 2 d Ser. IV. p. 347, pi. 
22, fig. 14. Bennet, Wiltshire, Foss. pi. 18, fig. 2. 
Transversely and obliquely longitudinal, its width nearly 
double its length, convex; posteriorly flattened; surfaco tu- 
berculate, set in curved series. 
The Portland Stone, Portland; Vale of Wardour and 
Swindon. 
22 . Trigonia impressa. —The Impressed Trigonia. 
T. impressa. Sowerby, Zool. Journ. III. p. pi. 11. fig. 1 . 
Sub-triangular, anterior side rounded ; posterior side some¬ 
what truncated, beaks obtuse ; surface with a series of con¬ 
centric papillose ribs. 
The Great Oolite, Stonefield. 
23. Trigonia literata. —Lettered Trigonia, pi. LXI.*** 
fig. 21. 
T. literata. Phillips, Geo. York, I. pi. 14, fig. 11 . 
Sub-triangular, sub-conic, moderately convex ; anterior side 
rather abruptly sub-truncated; posterior side concave above, 
considerably produced, and somewhat acuminated below, se¬ 
parated from the other portion by a longitudinal, linear row of 
obtuse tubercles, which emanate from the beak, and with an 
obscure longitudinal row of pustules in its centre, obliquely 
crossed by lines of growth; anterior portion of the surface 
with a series of very strong, rugged, longitudinal ribs, which 
rapidly thicken as they descend, emanating from the pus¬ 
tular division, which, on reaching the centro of the valve, 
suddenly turn upwards at an acute angle, in the form of the 
letter F, and again turn to the anterior margin ; all the ribs 
are crossed by irregular rough stria); beaks acuminated and 
incurved ; lunulo, large, and bounded by a margin of trans- 
versly elongated pustules : basal lino convex. 
The Lias, Robin Hood’s Bay, Yorkshire. 
Tribe III.—ARCACEA. 
Shells provided with numerous small primary teeth, dis¬ 
posed in a straight or interrupted line in each valve. 
Genus VII.—NUCULA.— Lamarck. 
Shell equivalve, inequilateral, transverse, oval, trigonal, or 
oblong; generally covered with a strong epidermis; hinge 
linear, narrow, divided into two parts by an oblique, produced, 
nearly central pit, which is destined for the reception of the 
ligament ; the one anterior, and the other posterior; lateral 
teeth on each side numerous, acute, elevatod, somewhat re¬ 
curved, those of the opposite valves locking into the inter¬ 
vening spaces; umbones contiguous, and not separated by an 
intervening area; two simplo, muscular impressions ; mantle 
impression destitute of a sinus. 
1 . Nucula ovalis. —The Oval Nucula, pi. LXXVI. fig. 
33. 
N. (?) ovalis. Murchison, Silur. Syst. pt. II. p. 609, pi. 5, 
fig. 8. 
Shell transversely ovate, smooth, rather convex ; beaks sub¬ 
acute, and placed near the anterior side ; length about four 
lines, breadth five lines. 
The Uppor Ludlow Rock, Trewerno Hills on the Wye, 
Radnorshire. 
2. Nucula l^evis. —The Smooth Nucula, pi. LXXVI. fig. 
22 . 
N. hvvis. Murchison, Silur. Syst. pt. II. p. 635, pi. 22, f. 1. 
Shell oval,transversely elongated,smooth, ventricose ; beaks 
large, acute ; length three-eighths of an inch, breadth two- 
eighths. 
Found in Black Schist, in the Lower Silurian Rocks, Pen- 
sarn, near Caermarthen, Wales. 
3. Nucula Cobboldi;e. —Cobbold’s Nucula, pi. LXXVI. 
fig. 55. 
N. Cobboldice. Sowerby, II. p. 177, pi. 180, fig. 2. 
Transversely obovate, convex ; posterior side very short, 
with numerous, shallow, smooth, zigzag furrows, diverging 
over the sides ; space between the teeth elongated and deep ; 
margin entire. 
The Mammiferous Crag, Bramerton, and the Red Crag, 
Sutton. 
4. Nucula lanceolata. —The Lance-shaped Nucula, pi. 
LXXVI. fig. 55. 
N. lanceolata. Sowerby, II. p. 178, pi. 180, fig. 1. 
Transversely lanceolate and ovate ; width double the length ; 
sides nearly equal, the auterior very slightly the largest; pos¬ 
terior side a little pointed ; beaks a little produced ; surface 
smooth ; hinge with a deltoidal concave space ; margin entire ; 
substance of the shell strong. 
The Red Crag, Bawdsey. 
5. Nucula deltoidea. — The Deltoidal Nucula, pi. 
LXXVI. fig. 51. 
N. deltoidea. Sowerby, VI. p. 103, pi. 554, fig. 1. 
Triangular, ventricose; anterior side short, and rounded; 
posterior side obliquely truncated, flat, and pointed ; generally 
smooth, but sometimes longitudinally striated towards the an¬ 
terior margin. 
The Upper Marie, Isle of Wight, and Bagshot Sands, Sliap- 
ley Heath. 
6 . Nucula inflata. —Tho Inflated Nucula, pi. LXXVI. 
figs. 11, 12. 
N. inflata. Sowerby, VI. p. 103, pi. 554, fig. 2. 
Almost globular ; the posterior side small, and a little pro- 
