268 
ORIGINAL ARTICLES. 
The closely allied genera Limnadia and Limnetis are known by 
the following species: 
Limnadia Hermanni, Ad. Brongn. 
Baird, Proceed. Zool. Soc., 1849, 
p. 86, Anmilos. pi. 21, fig. 1. 
— Mauritiana, F. E. Guerin. Ma¬ 
gas. de Zool, Sept. Annee, Class 
VII. p. 1—7, pi. 22 (21 in the 
text) figs. 1 —11 , 1837 ; Baird, 
Proc. Zool. Soc., 1849, p. 87. 
— Antillarum, Baird. Proc. Zool. 
Soc., 1852, p. 30, Annulos. pi. 
23, fig. 1. 
— coriacea, Haldemann. Proc.') 
Philad. Acad., 1842, vol. i. p. | 
184; and 1854, vol. vii. p. 34. }> 
Limnadella Kitei, Girard. Ibid., j 
1854, vol. vii. p. 3. J 
Limnetis brachyurus, Muller. En- 
tomogt., p. 69, t. 8. figs. 1—12. 
— Wahlbergii, Loven. Ofvers. k. 
Vet. Akad. Forh., Arg. 3. No. 
2, p. 57, 1847. 
— Gouldii, Baird. Proc. Zool. Soc. 
1862, p. 149, pi. 15, fig. 7. 
Freshwater pool, Fontainebleau ( Brong- 
mart). 
Mauritius (Julien Desjardins). 
San Domingo (Salle). 
(Probably the same). “ In ditches along 
the Susquehanna, in quiet water;” in 
“ roadside ditches”(S'. S. Haldemann). 
In fresh water, Cincinnati (T. Kite). 
Freshwater marshes, Denmark {Muller). 
Freshwater marshes, Natal (J. Wald- 
berg). 
Freshwater, at St. Ann's, twenty miles 
from Montreal ( C. Gould).* 
The recent JEstherice are found in fresh water ; rarely in brackish 
water. Guided by this fact, and taking for granted that our fossils 
were true Lstheriee, and that Lstherice always have had freshwater 
habitats, we should suppose that the deposits in which these fossils 
are found, free from any appearance of having been drifted, must 
have been formed in rivers, lakes, or lagoons. Applying, however, 
the same rules in judging of the nature of the fossil molluscs and 
other organic remains that occasionally accompany some of these 
JEstheriee , we must regard the Ling til a of the Old Led (of Livonia), 
the Spirorbis, the Aviculee, the AntliracosicB , and Anthracomyce j* of 
the Carboniferous shales, and the Lingula and JPleurophorus of the 
Trias, as truly marine shells. Many, however, of our fossil JEstheriae 
occur in strata destitute of any such evidence of marine conditions; 
and possibly the occasional mixture of the marine and freshwater 
organisms may have been the result of drifting (the free-swimming 
JEstJierice being readily swept away by a flood), or of very rapid 
changes of condition, such as might be brought about by the alter¬ 
nate occupation of a lagoon by sea- and river-water. J Seeing, too, 
* Dr. Baird has kindly assisted me in drawing up this table of the recent Es- 
tlierice and their allies. 
t According to Mr. Salter, ‘ Mem. Geol. Survey, 1861, Iron-ores of South 
Wales,’ See. 
J See Sir C. Lyell’s observations on the value of Spirorbis (in the fossil state), 
and barnacles (recent) in certain cases, as evidences of the occasional inroad of salt 
water into swamps, killing the marsh-plants and leaving behind such shells as the 
