NAYADES. 107 



1. Unio pictorum, pi. XIX, f. 1, 2, 3, 4. 



Unio pictorum, Lamarck, An. San. Vert., VI, p. 77 ; Ency. 

 Meth., pi. 248, f. 4; Pfeiffer, I, p. 1 15, pi. 5, f. 9, 10; Draper- 

 naud, Moll., pi. 11, f. 4 ; Rossmassler, I, pi. 3, f. 71, o, h ; lb., 

 Ill, p. 23, pi. 13, f. 197 ; lb., IX and X, p. 10, pi. 45, f. 587 

 to 590 ; Unio rostratus, Pfeiffer, I, p. 114, pi. 5, f. 8 ; Mya 

 pictorum, Sturm, Fauna, VI, p. 2, f. a; Schroeter, Flussconch., 

 pi. 4, f. 6; Wood, Conch., p. 104, pi. 19, f. 3, 4 ; Donovan, 

 Brit. Sli., Ill, pi. 89 ; Mya ovalis, Montagu, Test. Brit., p. 34 ; 

 Mysca pictorum, Turton, Man., p. 20, pi. 2, f. 11 ; Gray's Tur- 

 ton, p. 295, pi. 2, f. 11, badly figured; Unio pictorum, Brown, 

 Illust. Conch., p. 81, pi. 31, f. 7, 8, 9, 10, 11 ; lb.. First Ed., 

 pi. 26, f. 4. 



Shell thin, transversely oblong-oval, ventricose ; umbones a 

 little produced, and placed near to the anterior side, which is 

 short, and rounded ; posterior side elongated, and somewhat 

 pointed; hinge line slightly bent; basal line nearly parallel, and 

 a little hollowed in the centre ; hinge furnished with a strong, 

 double, compressed, elevated, elongated, crested, crenated, car- 

 dinal tooth in the left valve, with a perpendicularly papillose, 

 striated cleft on the side of its posterior portion, on which the 

 tooth of the opposite valve rests, which locks into a space above 

 the shorter cardinal tooth in the opposite valve; lateral teeth in 

 both valves long, narrow, and sunk at the umbones, — from 

 whence they take their rise, — becoming more elevated and 

 acute as they diverge, and extend the same length as the liga- 

 ment; inside highly pearlaceous; varying in different specimens 

 from bluish-white to a rich salmon-colour, with faint, nearly 

 obsolete radiations, extending from the umbones to the mar- 

 gins; pallial impressions well marked; anterior muscular im- 

 pressions very deep ; posterior ones distinctly defined ; outside 

 covered with a smooth, shining, yellowish-green epidermis, but 

 varying in colour from different locahties ; with very indistinct, 

 nearly obsolete, divergent grooves, radiating from the umbones 

 to the margins ; and with transverse, concentric, slight furrows, 

 and very irregular, transverse striae, most conspicuous towards 

 the sides. 



Fig. 7, pi. XXI, is an external view of the teeth of the 

 hinge. 



Found in the river Ouse, at York; (he Aire, near Gargrcw; 



