234 
CONCHIFERA. 
Transversely sub-oval; one side rounded, the anterior ono 
acuminated and folded back with a hollow behind ; a longi¬ 
tudinal furrow emanates from behind the reflection, and ter¬ 
minates on the margin ; posterior side nearly plain, or with a 
few concentric wrinkles ,* anteriorly with numerous thin un¬ 
dulating, sharp-angled wrinkles, and longitudinal divergent 
grooves, producing a reticulated appearance; inside with a 
large much curved tooth, below the umbonal region in both 
valves. 
The Pleistocene Marine Formation, ITouth, Ayr ; the Coral 
Crag, Sutton; the Red Crag, Walton; and Mammiferous 
Crag, Postdam. 
6. Piiolas eoNSTRiCTA.—The Constricted Pliolas, pi. 
XCIV. fig. 21. 
P. const ricta. Phillips, Geo. York, I. pi. 2, fig. 17. 
Transversely elongated; anteriorly short, rounded, and 
truncated ; posteriorly constricted and acuminated ; a furrow 
from the internal region to the base ; whole surface with longi¬ 
tudinal ribs. 
The Gault, Speeton, Yorkshire. 
7. Piiolas dactylus. —Date Pliolas, pi. XCIV. fs. 11, 12. 
P. dactylus. Brown, Ill. Rec. Conch. Brit. p. 115, pi. 4 9, 
figs. 1, 2, 3. 
Greatly elongated transversely ; umbonal region placed much 
to one side, reflected, with a series of cells externally, and 
covered with two concentrically striated valves ; posterior to 
them a long, spatuliform, accessorial valve ; surface anteriorly 
rough, with waved ribs decussated by longitudinal stria); pos¬ 
terior side smooth, with some shallow lines of growth. 
The Pleistocene Marino Formation, Ayr. 
8. Piiolas recoin'dita.— Recondite Pliolas, pi. XCIV. f. 22. 
P. recondita . Phillips, Geo. York, I. pi. 3, fig. 19. 
Transversely ovate, rounded at both sides, an oblique, longi¬ 
tudinal, nearly central furrow, transversely striated. 
The Coral Rag, Mai ton, Yorkshire. 
9. Piiolas papyraoea.— The Papyrus Pliolas. 
P. papyracea. Brown, Ill. Rec. Conch. Brit. p. 114, pi. 49, 
figs. 4, 6*, 7, 9. 
Transversely ovate, anterior side ventricose and rounded, 
closed when the valves are shut; posterior side acuminated, trun¬ 
cated, and with an accessory ring; each valve with an oblique, 
longitudinal groove, with coarse and parallel strim beyond it; 
posterior half with closer set, slightly oblique, crcnate ribs. 
The Coral Crag, Sutton. 
10. Pholas gigantea. —Gigantic Pliolas, pi. XCV. fig. l. 
P.gigantm. Sowerby. Goo.Tr, 2d Ser. IV. p. 338, pi. 14,f. 1. 
Transversely elongated; nearly cylindrical; antorior side 
short and rounded ; posterior side elongated and angular below; 
surface with oblique radiating furrows and ribs; margin 
crenated. 
The Gault, Folkstone and Lympne. 
Family IV.—'TUBICOLA. 
Animal contained in a testaceous sheath, distinct from its 
valves, incrusted entirely or in part in the wall of this tube, 
or projecting outwards. 
Genus LXX.—GASTROCILFNA.— Spengler. 
Shell equivalve, inequilateral, somewhat wedge-shaped ; au- 
torior side rounded, when viewed in front, and posteriorly 
acuminated ; antorior side gaping widely, its aperture being 
sub-ovate, and acute behind ; hinge marginal and linear, des¬ 
titute of teeth, but in their stead a small laminated appendage, 
emanating from the umbo, allied to the samo tooth-like pro¬ 
cess in the genus Pliolas ; ligament external. 
This shell is enclosed in a testaceous, irregular, claviform 
tube, situate at its broader extremity; it is open and attenua¬ 
ted anteriorly, with an oblong, bilobate aperture, which is 
nearly sub-divided by a projecting septum, that does not quite 
reach across the opening; theso serve for the passage of the 
two tubes of the animal; the posterior end of the tube is 
closed. This club-shaped tube is found either within the perfor¬ 
ated cavities of rocks, or in old shells or corals, the testaceous 
tube always protruding beyond the surface. 
1. Gastrocii/E.na contorta. —The Contorted Gastrochm- 
na, pi. XCVI. figs. 22, 23, 24. 
G. contorta. Sowerby, VI. p. 50, pi. 526, fig. 2. 
Sheath club-shaped, bent nearly at a right angle, its aper¬ 
ture divided by two opposite ridges ; valves ovate, elongated ; 
surfaco with very fine stria), the intervening lines wide, oval, 
and pointed. 
In the London Clay, Barton. 
2. Gastrocil-ena tortuosa. —The Tortuous Gastrochmna, 
pi. XCVI. figs. 29, 30. 
G. tortuosa. Sowerby, IV. p. 49, pi. 526, fig. 1. 
Its longest diameter four times the united depth of both 
valves, obliquely lanceolate, and twisted ; hinge line straight; 
surface nearly smooth. 
Inferior Oolite, Blue Wick, Robin Hood’s Bay. 
3. Gastroctlena pholadea. —The Pholas-liko Gastro- 
chcena, pi. XCVI. figs. 20, 21. 
G. pkoladia. Brown, Ill. Rec. Conch. Brit. p. 116, pi. 48, 
figs. 13, 14. 
Transversely sub-ovate and wedge-shaped ; broadly and 
widly gaping at the anterior side, from which it gradually de¬ 
creases until it reaches the opposite extremity; beaks rather 
prominent and obtuse ; hinge with an obscure, laminar, trans¬ 
verse tooth in both valves. 
The Coral Crag, Sutton. 
Genus LXXL—TERIDINA— Lamarck. 
Shell orbicular, and entirely external, equivalve, inequilater¬ 
al ; umboncs greatly incurved, and covered by a somewhat 
quadrangular, accessory process, which seems to be fixed to 
the valves in front of the beak, with a subulate process in 
frcuit, and gaping at both extremities ; anterior opening an¬ 
gular at the back, and the posterior rounded in front; tube 
thick, fistulous, posterior extremity smaller, and open, and 
nearly divided into two from an interior projection on both 
sides, and provided with an operculum ; anterior termination 
