28 TESTACEA. 



PLATE VI. 



FIG. 1. Shell empty. 



2. Animal, outline of the under surface. 



3. The same, after nature, slightly enlarged. 



4. Another specimen, under surface. 



Reproduction. The season of propagation extends from July, or 

 earlier, through a considerable portion of the year, at least during the 

 finer season. 



In the year 1812, I made some observations on this subject, from 

 specimens inhabiting the garden-well at Binns, which were repeated on 

 others collected in the same place in 1836, meantime availing myself of 

 those which could be obtained elsewhere. The most limited sphere is 

 occupied for ages by the same race of animals, in their successive gene- 

 rations. Perhaps many of those which are free do not wander far from 

 the spot of their nativity. 



The spawn of the Ancylus is deposited in small, clear gelatinous 

 spots, containing eight, or perhaps more, minute embryonic white specks. 

 There is much disparity in the period required for then' attaining matu- 

 rity, being twenty-three to forty-three days, which might almost indi- 

 cate some difference in species. 



From specimens collected on September 16, an elliptical spot of 

 spawn was produced on the 23d, containing two white specks. Each of 

 these was in its peculiar capsule or compartment, as manifested on the 

 27th. Plate VI. figs. 5, 6, the latter enlarged. The embryos had grown 

 much, though they were rather shapeless, twenty-three days after the 

 date of production ; they exhibited slight contraction and expansion ; 

 and their two black eyes were very distinct. The spawn being affixed 

 to the side of a glass vessel, left the sole or under surface of the animal 

 next the eyes, the apex of the shell projecting inwards ; now, the shell, 

 which was pale silvery grey, seemed to be fluted. Fig. 7, enlarged. 

 Both animals quitted the spawn in another week, having attained matu- 

 rity in thirty-three days. 



Two specimens having been committed to a vessel in the end of 



