126 MOLLUSCA. 
concentricis decussata; apice acuta, valde incurvata: apertura ovato- 
rotundata. 
Ancylus aduncus, Gouin ; Proceed. Boston Soc. Nat. Hist., 11. 210. 
June 1847. Expedition Shells, 41. 
SHELL very brittle, oval, conical, very faintly transparent; apex 
posterior, very prominent and strongly incurved, having numerous 
fine cost radiating from it the whole distance to the margin, decus- 
sated by minute transverse striations, which, traversing the costée, give 
the whole surface a closely reticulated aspect. Epidermis thick and 
adherent, of a dull, sap-green colour, projecting a little beyond the 
margin. Beneath this, the shell is of a pale yellow or straw-colour 
during life, turning after desiccation or exposure to the air to a dull 
white. Aperture ovoid, the posterior extremity slightly narrowed. 
Interior a dusky white, with a tinge of dull green reflecting through 
from the epidermis. 
Length five-fortieths ; breadth two-fortieths ; height three-fortieths of 
an inch. 
Abundant in mountain streams of Madeira, especially where there 
were little rapids, in which places they often cover the stones by hun- 
dreds, collecting in groups, one upon another, to the number, some- 
times, of eight or ten. Apex often eroded and chalky. It was very 
difficult to detach them from the rocks without fracture. Not being 
provided with boxes to carry them separately, very few reached Fun- 
chal in good order, and no opportunity was afforded of observing the 
animal. [J. Pp. c.] 
The very pointed, projecting, strongly-curved apex makes it to re- 
semble the aculeus of a rose. It is not unlike A. concentricus, D’Orb.; 
Amer. Merid., pl. 42, figs. 19, 20. 
Figures 495, 495 a, two views of the shell, enlarged; 495 4, natural 
size. 
AMNICOLA BADIA (Gould). 
Testa minuta, turrita, elongato-conica, badia: spira acuta, apice erosa, 
