HAL*. -ASTKHOI'ODA. PECTINIBRANCHIATA. 121 



?]>ira], elongated tongue, having numerous triangular 

 spiuclet.s ; foot elliptical, very large ; orifice of the pul- 

 u'louary cavity on the left side, close to the anus ; mantle 

 adherent to the shell all round. 



Shell elliptical, conoidal, with the point curved hack- 

 wards, and nearer the posterior end, thin, fragile, striate. 



The Ancyli adhere, like Limpets, to stones and plants 

 in running and still waters, and although pulmonated, 

 are very seldom seen out of it. 



1 . Ancylus Jluvidtilis. Oval Lid-Shell. 



Shell conoidal, with the point recurved, and nearer the pos- 

 terior end, diaphanous, slightly striated longitudinally, more 

 distinctly striated concentrically, pale yellowish-grey or horn- 

 colour ; the aperture oval ; the inside whitish, and highly 

 f.'d. Nearly a fourth of an inch long, two- fourths high. 



It varies somewhat in form, and greatly in the prominence 

 of its ridges, of which the longitudinal are sometimes strongly 

 marked. Old shells, in still water, sometimes have the margin 

 much expanded, considerably thickened, and a little reflected. 



The foot is broadly elliptical, pale grey ; the head oblong, 

 pale grey, minutely dotted with darker ; the flap broad and of 

 the same colour ; the tentacula depressed or flattened, some- 

 what triangular, obtuse ; the eyes black ; the body conical, 

 yellowish-grey, partly dotted with dark grey, olivaceous- 

 brown toward the apex. 



Abundant in brooks and rivers, on stones and plants, espe- 

 cially potamogetons ; occurs also in pools, as in those of the 

 granite quarries of Rubislaw and Hilton, and in mill-dams. 



Ancylus fluviatilis. Muller, Verm. Terrestr. el Fluv. ii. 201. 

 vlus fluviatilis. Drap. Moll. 4H. PI. 2. f. 23,24 Patella fluvi- 

 atilis. Mont. Test. Brit 482. Ancylus fluviatilis. Gray's Turton, 

 249. Ancylus fluviatilis. Flem. Brit A mm. 280. Ancylus fluvi- 

 atilis. Larnk. Syst vi. 2, 27. Patella fluviatilis. Mont Test. Brit. 

 4S2. Patella fluviatilis fusca, vertice raucronato, inflexoque. 

 Lister, Anim. Angl. 15 J. PL 2. f. 32. 



ORDER II. GASTEROPODA PECTINIBRANCHIATA. 



Respiratory apparatus a branchial cavity situated on 

 the back, containing two branchiae, composed of parallel 

 rows of laminae or fimbrise attached to its upper part, 

 L 



