RUPERT JONES ON THE FOSSIL ESTHERIiE. 
273 
instar rostri productum, dorso non tuberculifero. Pedum paria nu- 
mero ferine 21, foliaceorum. Abdomen fere acin Limnadia.” 
Limnetis . “ Antennae internae 2-articulatse. Cauda brevis, trun- 
cata, appendicibus facie inferiore destituta. Pedum paria 12.” 
The above-quoted diagnoses relate to the bodies and limbs of the 
three genera. In their carapaces they differ to some extent; Lim¬ 
netis and Limnadia having a less perfect hinge and little or no umbo, 
and being generally destitute of concentric ridges ; whilst in Estheria 
the carapace-valves have a definite hinge-line, well-marked umbones, 
and usually numerous distinct concentric ridges (boundary-lines of 
the periodic stages of growth of the carapace-valves). A reticulate 
sculpture ornaments the carapaces of the three genera; but in Es¬ 
ther ia this ornamentation is stronger, and often modified by short 
vertical and inosculating bars. 
The valves of Estheria are inequilateral, usually subtriangular 
or subovate; the umbo being almost always near the anterior end, 
and the edge of the valve and the parallel concentric ridges having a 
bolder curve posteriorly than in front. Occasionally, however, the 
umbo is almost central and the two ends of the valve nearly equal; 
the ventral edge of the valve and the concentric ridges having a 
nearly semicircular curvature. There are, however, numerous gra¬ 
dations of form between these extremes; so that I cannot see any 
grounds for a generic distinction being made between the subtrian¬ 
gular and the suborbicular forms on account of the relative position 
of the umbo.* * 
In three instances I find shortened or subquadrate forms of cara¬ 
paces accompanying others of subovate outline (E. striata , E. Man- 
galiensis, and E. elliptic a) . This difference of shape may be sexual, 
or due to conditions of growth. Dr. S. Pischer assigns a shorter 
carapace to the female of his E. Hierosolymitana f than the one belong¬ 
ing to the male. The squarer carapaces above referred to are rare 
among the subovate individuals ; some of the latter certainly contain 
what appear to be ova. 
Of Isaura cycladoides (Estheria gig as ) M. Joly has remarked that 
in its young state it undergoes certain successive changes of form, 
more or less analogous to the persistent conditions of “ Artemia , 
viai and the more readily, because, as I have elsewhere stated, I believe that in the 
case of appellations invented for groups of animals, plants, or minerals, whether they 
be names of genera, families, orders, or classes, it is not always priority that should 
determine the general use of such terms, but, either their adaptability, the precise¬ 
ness of their definition, or other advantageous characteristics, as the case may be. 
With “ specific” names, however, it is very different; the published name of a spe¬ 
cies is (or ought to be) not only the established appellation of a distinct form in 
nature, but also the registered evidence of the successful labour and acumen of its 
discoverer and describer. 
* Dr Pander has informed me that he considers Asmusia, of Pacht, to be gene- 
rically distinct from Estheria on this ground. 
f Abhandl. Akad. Wiss. Munchen, viii. pi. 20, fig. 8. 
N. H. R—1863. T 
