3MYA. CATER. 107 



the margin, irregularly striate transversely, a little con- 

 tracted or indented opposite the hinge on the front mar- 

 gin : heaks much worn and rugged, appearing as if worm- 

 eaten ; inside perlaceous mixed with green, and often 

 rough with pearly excrescences : hinge with a strong erect 

 tooth in one valve, locking between a widely cloven one in 

 the other : length nearly two inches, and four in breadth. 

 In rapid rivers, v. v. 



23. Mya insquivalvis. Unequal Gaper. 



Montagu, pi. 26. f. 7 Linn. Trans, viii. pi. 1. f. 6 

 Walter, f. 35. 



Shell somewhat triangular, produced on one side, strong, 

 convex, opake, covered with a brown skin, under which it 

 is \vliite with frequently a flesh-colored skin, the younger 

 ones marked with pale or flesh-colored rays ; one of the 

 valves much larger, regularly striate transversely with a 

 few deeper grooves, and folding over so as to receive the 

 smaller one ; the lesser valve obscurely striate transversely, 

 with a few longitudinal raised lines : beaks prominent, gib- 

 bous ; that of the larger valve turning over and meeting 

 the other : hinge with a strong pointed recurved tooth hi 

 the larger valve, and a cavity; in the lesser vuive is a 

 spool-shaped tooth projecting inwards, having a raised 

 denticle at the posterior side, and a cavity, all locking into 

 each other ; inside smooth, polished at the edge : length 

 about a quarter of an inch; breadth not half an inch. 



Western coasts, Scotland, Dublin bay. v. v. 



24. Mya Glycymeris. Great Gaper. 



Lister, pi. 414. f. 258 Donovan, pi. 142 /Pood, pi. 25. 



Shell large, coarse, lamellar, oblong-oval, irregular at 

 the margin, open at both ends, with regular w;\ved trr~?- 

 verse ridges disposed like bands, and marked with fine 

 striae, obliquely truncate at the anterior end: color yellow- 

 ish or ochrace >us, whitish within : beaks nearly ce- 



I both sides : hinge with a large thick tooth, 

 in one valve, besides a lesser one and a series of wri". 

 closing into a cavity in the other valve : length < 

 iuchoi. : !.?;-.?adla eight or nine. 



