o> 
Capt. Brown’s Monograph on the Pisidium. 413 
The animal is white, very tender, and pellucid ? length of the 
toot three lines ; breadth of the projection three-fourths of a line. 
_ Pfeiffer, Land-und-Was. Sch. p. 124, Pl. V. Figs. 19, 20. 
The shell nearly oval, with unequal sides, ventricose, irregular- 
ly triangular, and somewhat pellucid; beautifully striated con- 
centrically, having the appearance of ribs; the external colour 
yellowish-gray, the internal colour bluish; the beak a little ele- 
vated, pointing towards the anterior slope; length three lines, 
breadth between four and five lines; thickness two lines and a 
half. 
Inhabits rivers and streams. 
Cyclas obliqua, Lamarck An. san Vert. Tom. V. p. 559. 
Brown’s Ill. Brit. Conch. Pl. xvii. Fig. 14. 
Tellina amnica, Maton and Rackett in Lin. Tr. VIII. p. 
Cardium amnicum, Montagu, Test. Brit. p. 86. 
The latter author found it in the Avon, Wiltshire; and in 
water courses, near Wareham, Dorsetshire. I have found it in a 
small stream, which empties itself into the Water of Leith, at 
Colt Bridge, near Edinburgh. 
9. Diz StuMPFE ERBSMUSCHEL.—Pisidium obtusale. 


P. testa oblique cordata, ventricosa, tenuissime striata; pellucida, 
fragilissima ; umbone obtusissimo. 
Pfeiffer, Land-und-Was. Sch. p. 125, Pl. V. Figs. 21, 22. 
Shell oblique, ventricose heart-shaped, sides somewhat unequal, 
pellucid, very thin, with extremely minute concentric striz ; 
_ colour yellowish-white, or pale horn; the lower edges of the valves 
rather sharp ; the beak prominent, and obtusely rounded; length 
one line ; breadth one line and a quarter ; thickness three-fourths 
of a line. 
The animal is extremely pellucid, of a bluish-white ; and has the 
power of projecting the foot one line. Its powers of lecomotien 
are considerably rapid. 
This is new as a British species. I found it in great abundance 
in a ditch, at the Wells of Weary, immediately under the columnar 
greenstone rocks, west end of Arthur’s Seat, near Edinburgh. 
This habitat agrees with those of Pfeiffer, who says it is found in 
“* watery ditches.” 
Pfeitfer says, ‘‘ this shell, which is nearly related to the follow- 
ing species, was hitherto probably considered as a variety of the 
latter. Iam not quite sure whether Lamarck’s Cyclas obtusalis 
is the same as the species here described, as his description is very 
imperfect.” He states the magnitude of the Cyclas obtusalis to 
be four, and that of the Cyclas fontinalis to be two millemetres ; 
but of the shells here described again, my Pisidiwm fontinale is 
somewhat bigger than the Pisidium obtusale. 
3. Die QuELLEN-ErpsmuscHEL.—Pisidium fortinale. 
Described at page 11. of this Journal. 
