NAYADES. Ill 



5. Unio ovalis, pi. XVIII, f. 4, 5. 



Unio ovalis, Leach, MSS., p. 10; Mya ovalis, Montagu, Test. 

 Brit., p. 563; Mya depressa, Donovan, Brit. Sh., Ill, pi. 101 ; 

 Mya ovata, Donovan, Brit. Sh., IV, pi. 122, f. 1, 2, 3 ; Mysca 

 ovata, Turton, Man., p. 21, pi. 2, f. 12; Mysca solida, Turton, 

 Biv., p. 246, pi. 16, f. 2 ; l/nio tumidus, Rossmassler, I, pi. 14, 

 f. 204 ; Unio tumidus, var., Rossmassler, VIII, p. 4 1 , pi. 40, f. 

 542; Unio ovalis, Brown, Illust. Conch., p. 82, pi. 31, f. 12, 

 13, 14; lb.. First Ed., pi. 26, f. 2. 



Shell strong, thick, transversely ovate ; hinge line arcuated ; 

 umbones prominent, wrinkled, and closely approximate; right 

 valve with a strong, double, erect, cardinal tooth, the higher 

 portion situate immediately below the umbo, considerably 

 elevated above the margin, and two long, oblique, lateral 

 teeth ; muscular impressions of moderate size, the anterior 

 ones deep ; pallial impression deeply defined ; left valve with a 

 single, erect, oblique, cardinal tooth, and a long, elevated, lateral 

 tooth, which fits into the cleft between those of the opposite 

 valve; inside iridescent, and of a pale reddish-salmon colour, 

 and the posterior side of the valves often rough and irregularly 

 wrinkled; outside usually with strong, concentric hues of 

 growth, which are often fohaceous at the posterior side, and of 

 an olivaceous-brown colour ; the umbones generally redder, 

 and frequently with longitudinal radiations of pale yellow, or 

 bug". Length upwards of three-fifths of its breadth ; thickness 

 not two-fifths. 



Fig. 14, pi. XXI, external representation of the teeth. 



This species will be distinguished from the tumidus, by its 

 more oval form, and in the posterior side being less produced, 

 as well as by its teeth being thicker, the central portion of that 

 in the right valve not so acutely notched on its edge, and rather 

 more elevated ; and the shell is much less inflated. 



Found in the Aire, near Skipton ; the Ouse, above York; 

 the Severn, near Shrewsbury; at Kirkstal Bridge, near Leeds; 

 and in the canal, near Burnley. 



6. Unio Batavus, pi. XVIII, f. 6, 7, 8, and pi. XXI, f. 

 10, 11. 



Unio Batavus, Lamarck, An. San. Vert., VI, pt. 1st, p. 78, 

 No. 33; Nilsson, p. 112, No. 8; Pfeiffer, I, p. 115, pi. 5, f. 14; 

 Rossmassler, II, p. 20, pi. 8, f. 128, a, h; Drapernaud, pi. 11, 



