10 TESTACEOUS MOLLUSCA. 
GASTROCH ANA. 
Equivalve, somewhat wedge-shaped, néth a very large oval oblique 
posterior opening between the valves, the anterior extremity 
nearly closed; hinge linear marginal and without teeth. 
G. Cunrrrormis. Lam. 1.—Reeve.t. 20. f.4,5.—Sow. G. f. 
4, 5.—Pholas Hians. Gm. 3217.—D. p. 39.—Ch.f. 1678 to 81.— 
W.t. 2.f.11. Oval, thin, semitransparent, greyish white, with the 
valves converging above, convex in the middle and wedge-shaped be- 
low, with transverse arched strie ; hiatus oval and very large, occupy- 
ing two-thirds of the length : teeth very small. 1}.—W. Indies. 
G. Myrinoipes. Lam. 2.—Rump. t. 45. f. P. Oblong, 
anterior side truncated, and scarcely more than twice the length of 
the posterior ; excepting a raised pyramidal radiating anterior 
space, which is crossed by elevated narrow ribs and covered with a 
tawny epidermis, the shell is almost smooth. 13.—Is/le of France. 
G. Moniorrna.* Lam. 3.—Sow. G.f.1, 2,3.—Reeve. t. 20. f- 
1,2, 3.—Mytitus Amsicuus. D.p. 104.—Mya Dvusia. Pen. 
—Don. t. 108.—W. t. 2. f. 23.—G. Hians. Fe. p. 458.—G. 
Puoouapia. Turt. B.t. 2. f. 8,9. Small, thin, brittle, opaque, 
rounded at both ends and widely gaping on one side; pale brown 
and marked with concentric strie: beaks nearly terminal and 
rather prominent.— France, burrowed in stone. 
G. Truncata. Sow. Z. P. 1834. Oblong, anteriorly with a 
rounded off truncation, posteriorly very short, sub-acuminated ; 
striated and dirty whitish: an anterior thin lamellar epidermis. 
=,..12..—Panama. 
G. Ovata. Sow. Z. P. 1834. Ovate, whitish, with concen- 
tric strie, which are slender, lamellar, and following the shape of 


tooth and an internal rib proceeding from the umbo to the basal 
margin of each valve. Tro muscular impressions, the anterior 
large and obovate, the posterior smaller and situated near the 
edge of the dorsal margin. 
X. Dorsatis.* Turt. t. 2. f. 4, 5.—Somw. G.—Reeve. t. 22. 
-—Flem. p. 455.—Puotuas X. Desh in Lam. 6.p.47. Globular, 
thin, smooth, greenish yellow, gaping in front, the anterior part of 
the hinge margin produced ; umbones turgid and sub-callous ; a 
thickened inner girdle terminated by a tubercle surrounding the 
gape. This interesting species which forms sinuous perforations 
in wood is the link between Pholas and Teredo, approximating 
rather to the former in being without an exterior tube, and posses- 
sing a shield which is small and divided into tio. 
X. Guososa. Sow. Z. P. 1835. Globose anterior dorsal edge 
sloping, the accessory valves rather large. ¥,..2 — Valparaiso. 
oa 
