INTRODUCTION. 11 



dorso non tuberculifero. Pedum paria numero ferme 21, foliaceorum. Abdomen fere ac 

 in Limnadia." 



Limnetis. "Antennae internse 2-articulat3e. Cauda brevis, truncata, 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 ; Limnetis and Limnadia having a less perfect 

 hingement and httle or no umbo, and being generally destitute of concentric ridges ; 

 whilst in Ustheria the carapace- valves have a definite hinge-line, well-marked umbos, 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 Estheria 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 gradations of form between these extremes; so that I 

 cannot see any grounds for a generic distinction being made between the subtriangular 

 and the suborbicular forms on account of the relative position of the umbo. 



In three instances I find shortened or subquadrate, or rather suborbicular, forms of 

 carapaces accompanying others of subovate outline [E. striata, E. Mangaliensis, and 

 E. elliptica). This difference of shape may be sexual, or due to conditions of growth. 



cated by Audouin and Straus-Durckheim in the same year ; the former proposing, for the species brought 

 by M. Bravais from Oran, the name of Cyzicus ; and the latter, for that brought by Dr. Ruppell from 

 Abyssinia, the generic name Estheria. From the simultaneous publication of these two generic names, it 

 is difficult to decide which should stand ; and M. Joly, apparently feeling the difficulty, has proposed a 

 third name, taking as the type the species found by him at Toulouse, and caUing it Isaura. As M. 

 Audouin merely indicates the genus, without giving a description of either genus or species, whilst M. 

 Straus details at full length both generic and specific characters, and figures the typical species, I propose 

 adopting his name, and retaining the generic name Estheria, a name originally proposed by Dr. Ruppell 

 himself." 



I coincide with Dr. Baird's opinion as to the propriety of using the terra Estheria ; 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 preciseness 

 of their definition, or other advantageous characteristics, as the case maybe. With "specific" names, 

 however, the case is different ; the published name of a species 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. 



