264 
ORIGINAL ARTICLES. 
“ Cyclas” or “Venus” of older figures, but has a semi-orbieular Posi- 
donomya-like form. On the other hand, E. minuta has more of the 
Pisidium-shape than its old name “ Posidonomya” would indicate. 
The microscope, moreover, exhibits the peculiar superficial ornamen¬ 
tation so characteristic of the bivalved Crustacea, and wanting in the 
Mollusca ; but of this ornamentation of the Estherice we had at hand 
the published illustrations and descriptions, by Dr. W. Baird, in the 
‘ Zoological Society’s Proceedings,’ 1849, &c.; and by this author and 
other carcinologists the animals of Estheria and its allies, the Lim- 
nadia and Limnetis , had been already fully made known. Another 
important result of the application of the microscope to these once 
obscure organic remains was the determination of the intimate struc¬ 
ture of the shell as belonging to crustacean and not to molluscan 
organisms. Whilst the shell of Posidonomya Becheri of the Lower 
Carboniferous rocks, and of JP. Bronni of the Lias, is truly of the 
molluscan type,* * * § that of the so-called Posidonomya minuta and its 
allies is crustacean. 
One of the fossil Estherioe (E. tenella , passing under the name 
of Posidonomya) was regarded by Agassiz, in 1845, and by JNaumann, 
in 1848, as being related to Cypris; Dr. Volger, in 1846, suggested 
of another ( E . minuta') that it might be a bivalved Crustacean ; and 
another (E. ovata ) was suggestively referred to Cypris and its allies 
by Lyell and Morris in 1847. 
In 1856 the Kev. W. S. Symonds, P.Gr.S., favoured me with some 
well-preserved specimens of the little Triassic Estheria f from Pen- 
dock, Worcestshire; and with the late Prof. J. Quekett’s kind assis¬ 
tance I was enabled to see, most distinctly, the true, crustacean cha¬ 
racter of the texture of its valves under the microscope. This con¬ 
firmed an opinion I had long held, and which had been previously 
advanced by Agassiz and Naumann, J by Volger § and by Lyell and 
Morris, || that some of the little fossils known as Posidonomyce are 
not molluscs, but closely allied to Limnadia , Limnetis , and Estheria , 
bivalved phyllopodous Crustaceans (Entomostraca ) of the present 
* Having the late Professor Quekett’s authority in deciding the molluscan 
character of a shell of the Lower Carboniferous Posidonomya from Northumber¬ 
land, which we examined together under the microscope, I cannot agree with Mr. 
J. W. Salter in thinking it probable that the great Posidonomyce of the Carbonife¬ 
rous rocks are crustacean, as suggested in his paper in the Annals Nat. Hist. 3rd 
ser. 1860, vol. v. p. 153. 
f This is the little Triassic shell that has been termed Posidonia , and Posi¬ 
donomya, minuta; Posidonia minuta (Alberti), Goldfuss; Posidonomya minuta , 
Bronn, Zieten { Strickland, and others. In Morris’s Catalogue of British Fossils, 
and edit. 1854, it is included in the Crustacea { as Estheria minuta ); but (appa¬ 
rently from inadvertence) it has not been expunged from the list of molluscs in that 
work. 
X Bullet. Soc. Geol. France, 2nd ser. vol. v. p. 301, and vol. vi. p. 90. 
§ Neues Jahrbuch f. Min. 1846, p. 818. 
J| Quart. Jour. Geol. Soc. vol. iii. p. 275, and Lyell’s Manual of Geology, 5th 
edit, p, 332. 
