120 LIMNiEID.^. 



A. Body sinistral. Shell dextral. 



1. Ancylus fluvia'tilis*, Miiller. 



Ancylus fluviatilis, Miill. Verm. Hist. pt. ii. p. 201 ; F. & H. iv. p. 18G, 

 pi. cxxii. f. 4. 



Body slate-colour or dark grey, with fine black specks : 

 tentacles somewhat triangular at the base, becoming slender 

 towards their tips, which are blunt : eijes not very prominent, 

 but distinct : foot oval, nearly equal in circumference to the 

 mouth of the shell. 



Shell semi-oval, incurved towards the front like a helmet 

 of the ancients, rather thin, not glossy, yellowish -grey or horn- 

 colour, strongly and regularly striate longitudinally in a radi- 

 ating direction from the crown to the margin or outer edge of 

 the mouth (some of the striae often forming remote ridges) and 

 very finely striate transversely or in the line of growth : anterior 

 margin somewhat narrower than the other : epidermis rather 

 thin : spire forming the beak and being equal to about half a 

 whorl, with a compressed and blunt top, which turns a little 

 to the right, bending down towards and nearly reaching the 

 posterior margin : mouth oval : outer lip membranous, slightly 

 reflected. L. 0-3. B. 0-233. 



Yar. 1. Capuloides. Shell larger and higher, with the beak 

 not placed so near the posterior margin. L. 0*415. B. 0*3. 

 A. Capuloides, (Jan) Porro, Mai. Com. p. 87, pi. 1. f. 7. 



Yar. 2. gihhosa. Shell smaller, more swoUen, with the 

 beak reaching or overhanging the posterior margin. A. gih- 

 bosus, Bourguignat in Journ. de Conch, iii. (1853) p. 186. 



Yar. 3. alhida. Shell milk-white and more finely striated. 



Habitat : Abundantly on stones and rocks in shallow 

 rivers and streams everywhere from Aberdeenshire to 

 the Channel Isles. I once found it of a dwarf size on 

 the leaves of the white water-lily in a stagnant pond 

 near Swansea, into which no stream had flowed within 

 the memory of man, living in company with A. lacustris, 

 and coated with a confervoid growth. Yar. 1. R. Corfe, 



^ Inhabiting rivers. 



