7 
(a) The cardinal teeth contiguous to the anterior end. 
Plate II. Fig. 13. S. truncatus. (Dillwyn.) 
(b) The cardinal teeth a little removed from the anterior end. 
Plate Il. 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.) 
Panopaa.—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 Cah. ] 
2. Hinge of ditto. 
GuycyMeris.—Shell transverse, gaping much on each side; hinge callous, without teeth ; 
nymphe 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.) 
(b) Hinge of ditto. 
SECTION II.__CONCHIFERA TENUIPEDA. 
The lateral gaping inconsiderable. 
‘Tue 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. 
