TESTACEA. 51 



many of them, prove extremely embarassiiig to the practical naturalist, 

 who would identify the subject with that of his fellows. 



Perhaps this may not be of equal use in a work designed as much 

 for the elucidation of certain physiological points as for systematic ar- 

 rangement. 



Diameter three lines ; volutes four, but only three are distinctly 

 visible. Orifice slightly oblique, considerably wider than the last volute 

 in large specimens. The circular exterior of the volute is plain and unin- 

 terrupted by any keel or projection. Both sides of the shell are some- 

 what concave, owing to the decreasing diameter of the volutions, as more 

 remote from the orifice. The animal a Umax, with a sole about a line 

 long, rather triangular, and a rounded shoulder ; the tentacula slender 

 and pointed, with a black eye rather towards the front of the head at the 

 external root of each. Shell light horn colour : sometimes, however, 

 almost black. Animal darker than the shell ; sole very dark. 



This creature feeds readily on the Eqnisctum, and, I believe, also on 

 the Veronica Beccabunxja. 



On September 6, I took thirty specimens from Coldingham Loch. 

 Their shells became much purer and cleaner in three weeks, owing both 

 to the food and to absence of muddy matter ; and at the end of the fourth. 

 the animals were exposed as transparent, and of a faint reddish colour. 



Two spots of spawn, extremely transparent, were now observed in 

 the vessel. One of them contained the embryos, some of which came to 

 maturity, and escaped after an interval of from seventeen to twenty- 

 seven days. The same period was confirmed by the observations of 

 another year. 



Fine specimens may be found under the chain bridge crossing the 

 river Tweed, a few miles south of Berwick. 



Specimens have survived above a year in my possession. 



PI.^TE XI. 



Fig. 3. Planorhis rhomheus. 

 4. Spawn. 

 .3. The same, enlarged. 



