30 TESTACEA. 



cessible, or from which they cannot be easily dislodged, the observer 

 may obtain their transference, by merely inverting it in a more conve- 

 nient vessel. The}' will descend slowly and gradually. But he must 

 beware of allowing them to remain too long dry, which can be prevented 

 by introducing a little water, and repeating the inversion of the phial 

 until the creature quits it. 



3. Ancylus lacustris. — Plate VI. Figs. 18-21. 



Some authors seem to have confounded this species with the pre- 

 ceding, though the difierence between them may be readily recognised 

 on inspection of both at once. 



Length of the shell two lines, breadth one, circumference of the 

 orifice a long oval ; the apex is considerably off the centre of the shell, 

 being nearer one extremity ; colour brown. This animal resembles the 

 former ; but it is smaller than the shell. Tentacula two. There are 

 also two active flexible organs, curving downwards and over the body, 

 as if in a searching manner. Eyes two, black, far apart. — Plate VI., 

 fig. 18, Ancrjlm lacustris, viewed from above ; fig. 19, under surface. 



This animal feeds on the interior of the leaf of the common yellow 

 Iris, and has occurred to me only in lakes and ponds. 



Several specimens taken on June 25, from the leaves of the yellow 

 Iris, were deposited in two separate vessels. On July 8, spawn was dis- 

 covered, but of such absolute transparence, that it might have been pro- 

 duced some days previously, and have escaped observation. Now it 

 would have passed unnoticed, unless for its resistance of the finger as a 

 liard substance on the surfiice of the glass. B}' closer inspection, spawn 

 was found on the sides of the vessel. 



This spawn consists of transparent, hardish, round spots, containing 

 i'rom two to eight embryos. I have seen more with only one. Their 

 presence and aspect may be descried by shifting the position of the 

 vessel, until suitable incidence of the light is obtained for exjiosure. 



Each embryo, as before, occupies its own capsule, integument, or 

 ovum. 



In early stages the embryos were just discernible amidst the spawn ; 



