104 NAYADES. 



Variety 8. Ponderosa, pi. XV, f. 1,2, 3. 



Anodon ponderosa, PfeiiFer, II, p. 31, pi. 4, f. 1 to 6; Ross- 

 massler, IV, p. 24, pi. 20, f. 282 ; Brown, Illust. Conch., p. 80, 

 pi. 30, f. 1 , 2, and pi. 29, f. 3 ; Mj/tilns Cygneus, var. /3, Maton 

 and Rackett, Linn. Tr., VIII, p. 109, pi. 3 a, f. 3. 



Shell large, thick, ponderous, rhombic-oval, very ventricose ; 

 externally wrinkled ; with the epidermis rough, fibrous, and 

 semivillous at the rounded anterior extremity, and at the base ; 

 posterior side long, subrostrated, and subtruncated at its extre- 

 mity ; base but slightly bent, or nearly parallel ; hinge line 

 considerably arcuated, with a long ligament, from whence it 

 somewhat abruptly descends ; beneath the ligament a sinuated 

 groove, rising abruptly, and forming a ventricose disk; umbones 

 rather tumid, and decorticated ; the ligamentary sinus small, 

 subcordate; inside bluish-white. Length two inches and three- 

 eighths ; breadth four inches and five-eighths ; thickness two 

 inches and a half. 



I was favoured with this interesting variety by my friend Mr. 

 Henry Johnson, Curator of the Museum, Royal Institution, 

 Liverpool, who found it at Otterspool, Aigburth, on the pro- 

 perty of John Moss, Esq., who has since most kindly supphed 

 me with a complete series for investigation. It also occurs in 

 Loch End, near Edinburgh. Another handsome variety of this 

 shell inhabits the lake at Rolleston, the seat of Sir Oswald 

 Mosley, Bart., near Burton-upon-Trent, to whom I am indebted 

 for a fine series of specimens. 



The latter variety is somewhat more acuminated in the beak- 

 ed side, and devoid of the villosity of the Otterspool variety, in 

 which respect it agrees with that found at Loch End. 



This shell has been mistaken for the A. Avonensis, by some 

 British Naturahsts. It is, however, considerably more inflated, 

 in proportion to its size, and a third larger. « 



Variety 9. Subrhombea, pi. XVI, f. 3, 4. 



Anodon subrhombea, Brown, MSS.; lb., Illust. Conch., p. 80, 

 pi. 30, f. 3, 4 ; Anodonta piscinalis, var. ? Rossmassler, VI, pi. 

 30, f. 416. 



Shell thick, subrhomboidal, rather inflated ; anterior side 

 slightly produced ; hinge line nearly parallel, and ascending 

 towards the posterior side ; ligament long, subarcuated, from 



