120 



A. Body sinistral. Shell dextral. 

 1. ANCYLUS FLUVIA'TILIS*, Miiller. 



Ancylua fluviatilis, MiiU. Verm. Hist. pt. ii. p. 201 ; F. & H. iv. p. 

 186, 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 : eyes 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 

 horncolour, strongly and regularly striate longitudinally in 

 a radiating 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. 



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

 not placed so near the posterior margin. L. 0415. B. 0*3. 

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



Var. 2. gibbosa. Shell smaller, more swollen, with the 

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

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



Var. 3. albida. 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. Var. 1. R. Corfe, 



* Inhabiting rivers. 



