( 16) 



DIVISION X. NAIADES. 



GENERA. 



L Unio. Brug. F. 



Equivalved, inequila- 2 teeth on each valve ; 

 teral ; beaks naked, worn : one cardinal, short, irre- 

 epidermis greenish or gular, simple or divided 

 brown ; sometimes a little in two, sub-striated; 

 gaping. Fig. 55. the other elongated, 



compressed, lateral. 



Ligament exterior, 

 posterior, muscular im- 

 pression composite. (1) 



Cardinal tooth short, thick, neither crested nor sub-striated. 

 £. •■ compressed, projecting, and frequently crested. 



2. Hyria. Lam. F. 



Equivalved, obliquely Hiuge with 2 creeping Ligament exterior, li- 

 trigonal, auriculated, base teeth; 1 cardinal, divid- near. (2) 

 truncated and straight. 

 Fig. 54. 



ed into 

 verging 

 rior the 



numerous di- 

 the inte- 



smallest ; the 



& P arts 



3. Anodon. Bmg. F. 



Equivalved, inequilate- 

 ral, beaks naked. Fig. 53. 



other lateral, very long, 

 and lamellar. 



Hinge linear ; no 

 tooth ; a cardinal plate, 

 smooth, truncated or 

 forming a sinus at the 

 anterior extremity, ter 



Ligament exterior, li- 



near 



entering 



at one 



end into the sinus of the 

 cardinal plate ; muscu- 

 impressions 



lar 



wide 



minating the base of the apart, sub-geminate. (3) 

 shell. 



a. No distinct angle at the posterior extremity of the cardinal line. 

 j8. A . • h •• •• 



4. IridinA. Lam. F. . 



Equivalved, inequilate- Hinge long, linear, Ligament exterior, 

 ral • beaks small, almost lessened in the middle, marginal ; muscular im- 

 Fig. 52. tuberculous, almost sub- pressions like those of 



crenated ; tubercles nu- the Anodon. (4). 

 merous and unequal. 



(1) These shells exist in the rivers of Europe and both Indies ; they are buried 

 in the mud, with their beaks downwards : many of them furnish good pearls. 

 Foss. in Gravel, Alluvial Clay, Sand, Coal-shale, Crag Marl, Portland Rock, Blue 

 Lias, Yellow Limestone. The plate should be turned to view the figure of the 

 Unio. Having received a better specimen after the first was engraved, I could 

 only enlarge the characters to give them more force, which 1 fear has produced 

 confusion, by making the figure too large for the space it occupies in the plate. 

 The lower part of the valve Fig. 55, fits into the upper part of the valve, Fig. 55 a- 



(2) The habitat is unknown. 



(3) They live in fresh-water lakes and ponds, under the mud at the bottom; 

 they are not eaten on account of their insipid taste. There is a genus of serpents 

 named Anodon (v. Dictionaire des Sciences Naturcllcs), but as the shell appears to 

 have the prior claim, I have not altered the name but merely corrected it, the 

 French Conchologists having, unaccountably, written it in the accusative 

 Anodonta. 



(4) It lives in the rivers of warm climates, and when it is deprived of its epi- 

 dermis, both the inner and outer surfaces present a beautiful appearance, the 

 mother of pearl being of a reddish hue and reflecting the colors of the rainbow. 



