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Pinna. — Shell longitudinal, wedge-shaped, equivalve, gaping at the summit, pointed at 
the base, the beaks straight: hinge lateral, without teeth. Ligament marginal, 
linear, very long, almost internal. 
Plate XI. Fig. 4. P- muricata. (Idem. — Linn.) 
MALL ACE A. — 5 Genera. 
Ligament marginal, sublinear, either interrupted hy indentations or serial teeth, or wholly simple. 
Shell subinequivalve, foliated. 
Crenatula. — Shell subequivalve, flat, lamellated, rather irregular ; no particular open- 
ing or pit for the byssus : hinge lateral, linear, marginal, indented ; indentations 
serial, callous, hollowed into pits, which receive the ligament. 
Plate XI. Fig. 3. C. mytiloides. 
Perna. — Shell subequivalve, flattened, rather deformed, texture lamellar: hinge linear, 
marginal ; composed of furrow-like, transverse, parallel, non-entering teeth, be- 
tween which the ligament is inserted. A posterior sinus, slightly gaping, situat- 
ed at the extremity of the hinge for the passage of the byssus; sides callous. 
Plate XI. Fig. 6. P. epliippium. (Ostrea epliippium. — -Linn.) 
Malleus. — Shell subequivalve, rude, deformed, mostly elongated, sublobate at the base; 
beaks small, diverging: hinge without teeth; an elongated conical pit situated 
under the beaks, traversing obliquely the facet of the ligament. Ligament partly 
external, short, inserted in the sloping facet of each valve. 
Plate XI. Fig. 7- M. albus. 
Avicula. — Shell inequivalve, fragile, rather smooth ; base transverse, straight; the ex- 
tremities produced, the anterior caudiform or tail-like ; a sinus in the left valve : 
hinge linear, unidentate ; a cardinal tooth in each valve under the beaks. Facet 
of the ligament marginal, narrow, channelled, not traversed by the byssus. 
Plate XI. Fig. 8. A. crocea. 
Meleagrina. — Shell subequivalve, rotundate, nearly square, externally squamose; the 
inferior cardinal margin straight, not caudate anteriorly ; a sinus at the posterior 
base of the valves for the passage of the byssus; the left valve being at this place 
narrow and channelled: hinge linear, without teeth. Facet of the ligament mar- 
ginal, elongated, nearly external, dilated in the middle. 
Plate XI. Fig. 9. M. margaritiferus. (Mytilus margaritiferus. — Linn.) 
TD 2 
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