MOLLUSCA. 
82 
ascending rather abruptly towards the posterior side, and form- 
ing a subrostrated termination ; umbones prominent, placed 
very near the anterior side, which is short, and rounded ; pos- 
terior side slightly gaping, much elongated, but not subrotund 
and subangulated ; produced by the somewhat elevated ridge, 
which diverges from the umbones to the extreme point of the 
valve ; cardinal teeth small, compressed, minutely serrated ; 
double, and lamelliform, elongated in the left valve, with a 
deep, perpendicularly sulcated sinus in its side, for the recep- 
tion of the tooth of the right valve ; the portion of the tooth 
next the umbo somewhat acute ; lateral tooth long and double 
in the left valve, single and sunk towards the umbo, and nearly 
parallel ; lateral tooth of the right valve single, depressed 
towards the umbo, but ascending, and more acute, as it 
diverges from the umbo ; inside bluish-white, and iridescent ; 
muscular impressions very deep ; pallial impression well defined ; 
outside of a dark olive-green, and with rather deep, concentric 
wrinkles. 
Figs. 3 and 4, pi. XXXII, exhibit the external and internal 
appearance of the teeth. 
This species differs from U. pictorum, in'its general length 
being more uniform, and in being broader at the posterior 
side, and less acute ; in the teeth being much smaller, and less 
elevated, as well as in the crenulations on their upper side 
being less distinct, and less regular ; in the shell being much 
thicker, and its posterior side being considerably shorter. 
Found in the Wharf, near Ottley; the Aire, near Keighley; 
the Wharf, near Bolton Bridge; and the Don, near Sheffield. 
3. Unio bostrata, pi. XXXII, f. 9, 10, 11, 12. 
Unio rostrata, Kokeil Museum; Alder, Mag. Zool. and Bot., 
II, p. 118; Lamarck, An. San. Vert., VI, pt. 1st, p. 77, No. 
31 ; Unio elongatata, Pfeiffer, II, p. 35, pi. 8, f. 5, 6 ; Unio 
pictorum, var., Nilsson, I, p. 118, f f; Ib., Ill, p. 23, f f; Ross- 
massler, VI, p. 55, pi. 29, f. 409- 
Shell greatly elongated transversely ; umbones very flat, 
placed near the anterior side; hinge line but very little 
arcuated, as far as the extremity of the lateral teeth, from 
whence it suddenly slopes both above and below, termina- 
ting in a somevvhat rostrated form ; basal line nearly parallel ; 
primary teeth rather thick, and serrated at the edge; lateral 
teeth long, and considerably elevated; anterior muscular im- 
pression moderately sized, and deeply sunk ; below the 
umbones, there are indications of remote, nearly obsolete 
striae ; internal surface of a bluish-white, with iridescent reflec- 
tions. Length not a third of its breadth ; thickness four-fifths 
of its length. 
Figs. 11 and 12, pi. XXXII, external and internal represen- 
tation of the teeth. 
This shell tapers more abruptly in thinness towards the pos- 
terior side, than any of its British congeners ; and is consider- 
ably more obtuse at its anterior side, than the U. pictorum ; but 
its much more elongated form, will at once distinguish it from 
that shell. 
I found this species in the canal, near Hull; and William 
Thompson, Esq., of Belfast, procured it in the Avon, near 
Leamington. 
4. Unio tumidus, pi. XXXII, f. 5, 6, 7, 8. 
Unio tumidus, Retzius, Nova Testaceor. Genera, p. 17, No. 
3 ; Unio tumida, Pfeiffer, II, p. 34, pi. 7> f* 2, 3, and pi. 8, f. 
[Nayades. 
1, 2 ; Rossmassler, II, p. 117, ph 3, f. 70 h ; Ib., Ill, p. 27, pi. 
3, f. 202, 203; Alder, Mag. Zool. and Bot., II, p. 118; Mysca 
solida, Turton, Man., p. 22, pi. 2, f. 13; Ib., Conch. Diet., p. 
246, pi. 16, f. 2. 
Shell very thick, solid, cuneiform, transversely oblong-ovate, 
much inflated ; umbones produced, and placed very close, situate 
near one extremity; anterior side short, rounded; posterior side 
long, gradually sloping from the umbones both above and below', 
and terminating in a subtruncated beak ; cardinal tooth large, 
single, thick, elevated, and finely serrated at the edge, in the 
right valve, and double in the opposite valve ; muscular im- 
pressions small, and deeply sunk both before and behind; pallial 
impression strongly defined; external surface with rather strong, 
concentric wrinkles, and the whole of a reddish-brown, slightly 
tinged with olivaceous-green ; inside white, with but little iri- 
descent lustre. Length half its breadth ; thickness four-fifths 
of its length. 
Figs. 7 and 8, pi. XXXII, external and internal representa- 
tion of the teeth. 
Found in the New River, near London ; and the Avon, near 
Leamington, Warwickshire. 
5. Unio ovalis, pi. XXXI, f. 12, 13, 14. 
Unio ovalis, First Ed., pi. 26, f. 2; 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 ; Unio tu- 
midus, Rossmassler, I, pi. 14, f. 204; Unio tumidus, var., Ross- 
massler, VIII, p. 41, pi. 40, f. 542. 
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 lines of 
growth, which are often foliaceous at the posterior side, and of 
an olivaceous-brown colour ; the umbones generally redder, 
and frequently with longitudinal radiations of pale yellow, or 
buff". Length upwards of three-fifths of its breadth ; thickness 
not two-fifths. 
Fig. 14, pi. XXXI, 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. XXXI, f. 3, 3,* 4, 5, 6. 
Unio Batavus, First Ed., pi. 26, f. 3; Lamarck, An. San. 
Vert., VI, pt. 1st, p. 78, No. 33; Nilsson, p. 112, No. 8; Pfeif- 
fer, I, p. 115, pi. 5, f. 14; Rossmassler, II, p. 20, pi. 8, f. 128, 
