7 
(a) The cardinal teeth contiguous to the anterior end. 
Plate II. Fig-. 13. S. truncatus. (Dillwyn.) 
( h ) The cardinal teeth a little removed from the anterior end. 
Plate II. Fig - . 14. S. cultellus. (Idem. — Linn.) 
(c) The cardinal teeth nearer the middle than the anterior end. 
Plate II. Fig. 15. S. radiatus. (Idem. — Linn.) 
Panopaja. — Shell equivalve, transverse, unequally gaping at the sides: one cardinal coni- 
cal tooth in each valve; and near it a short, compressed, ascending callosity, not 
projecting outwards. Ligament exterior, on the longest side of the shell, fixed 
to the callosities. 
Plate III. Fig. 1. P. Aldrovandi. (Mya glycymeris. — Gmelin.) [Mrs. Mawe’s Cab.] 
2. Hinge of ditto. 
Glycymehis. — Shell transverse, gaping much on each side; hinge callous, without teeth: 
nymphas projecting outside. Ligament external. 
Plate III. Fig. 3. G. siliqua. (Mya siliqua. — Chem.) 
4. & 5. Inside of ditto. 
MYARIA.__ 2 Genera. 
Ligament internal; having one large spoon-shaped tooth in each valve or in one only ; to the cavity 
of which the ligament is attached. The shell gapes at one or both sides. 
Mya. — Shell bivalve, transverse, gaping at each end; having one large cardinal tooth in 
the left valve, broadly compressed, rather rounded, and projecting almost verti- 
cally: a cardinal pit in the other valve. Ligament internal, inserted in the pro- 
minent tooth and the corresponding pit. 
Plate III. Fig. 6. M. truncata. (Idem. — Linn.) 
7. Inside, shewing the hinge of ditto.. 
Anatina. — Shell transverse, nearly equivalve, gaping at one or both sides; one naked, 
broad, spoon-shaped cardinal tooth, projecting internally in each valve, and re- 
ceiving the ligament. In many species, a lamina or falcated rib runs obliquely be- 
low the cardinal teeth. 
Plate IV. Fig. 1. (a) A. myalis. (Mya declivis. — Pennant.) 
(&) Hinge of ditto. 
SECTION II CONCHIFERA TENUIPEDA. 
The lateral gaping inconsiderable. 
The shells of this section compose Four Families, which are separated into Two Divisions, 
viz. — 1. Mactracea and Corbulea, having the ligament internal, with or without any 
external ligament.™ — And, 2, Lithophaga and Nymphacea, having the ligament 
always external. 
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