568 



IMBEDDING OF AQUATIC SPECIES 



[Ch. XLVIII 



smaller 



some 



(fig. 141, h, c), as is seen 

 species. In the stems of 



several species, however, there is only a single tube."^ 



The valves of a small animal called Cypris {G. ornata ? Lam.) 

 occur completely fossilised, like the stems of Charge, in the 

 Scotch travertin above mentioned. The same Cypris in- 

 habits the lakes and ponds of England, where, together with 

 many other species, it is not uncommon. Although extremely 

 minute, they are visible to the naked eye, and may be observed 

 in great numbers, swimming swiftly through the waters of 

 our stagnant pools and ditches. The antennae, at the end of 

 which are fine pencils of hair, are the principal organs for 



J, and are moved with great rapidity. The animal 



swimmm 



rig. 142. 



Fig. 143. 



Cypris umfasciatay a living species, greatly 



magnified. 



Cypris vidua, a living species, 

 greatly magnified, f 



a. Upper part. 



b. Side view of the same. 



resides within two small valves, not unlike those of a bivalve 

 moUusk, and moults its integuments annually, which the 

 conchiferous mollusk does not. The cast-off shells, resem- 



bling thin scales, 



and occurring in countless 



mj 



many 



freshwater 



mar 



impart to them a divi- 



om 



mica. 



The recent strata of lacustrine origin above alluded to are 

 of very small extent, but analogous deposits on the grandest 

 scale are forming in the great Canadian lakes, as in Lakes 

 Superior and Huron, where beds of sand and clay are seen 



On Freshwater Marl, &c. Ey C. p. 73. 

 Lyell, GeoL Trans., vol. ii., second series, f See Desmaret's Crustacea, pi. 55. 



! 



I 



