ESTHERIA MINUTA. 43 



Carapace convex, compressed-oviform, like a Pmdium. 1 Carapace-valves more or less 

 oblong, with rounded corners, or subovate ; varying in outline from subquadrate (PI. I, 

 fig. 28) to irregular ovate (PI. II, fig. 1). The hinge-border is straight, but varies some- 

 what in relative length, sometimes falling away quickly into the curve of the posterior border 

 (as in PI. II, fig. 4), sometimes equal to two thirds the length of the valve ; the umbo is 

 placed forwards, at the end of the hinge-border, and the anterior margin curves away in 

 front of it, with a bold, semicircular outline. The ventral border is more or less convex, 

 usually symmetrical, but sometimes oblique (PI. II, figs- 1 and 5), trending upwards pos- 

 teriorly ; the hinder margin is rounded, like the anterior, but it is longer, more contracted, 

 and less obtuse, giving an obliquely ovate outline to the valve, which is highest anteriorly, 

 whilst in E. striata, E. Mangaliensis, and E. Murchisonia, it is highest posteriorly. Figs. 

 2 and 6, PI. II, show the lateral convexity of the carapace to be greatest just behind and 

 below the umbo, in the anterior third of the shell. Between the concentric ridges (which 

 are about 14 in number and upwards), the carapace bears a reticulate ornament 2 of irregu- 

 larly hexagonal meshes, 5 to 7 of which may be traced from ridge to ridge ; the size of 

 the meshes and the thickness of their walls varying very much in different specimens 

 (PI. I, fig. 30, and PI. II, figs. 3 and 7), according to the degree of fossilization and wear, 

 for the most part. 



The best specimens which have afforded me exact information as to the form, structure, 

 and features of the carapace of Estheria minuta are from Pendock, Worcestershire (PI. II, 

 figs. 1 — 3) ; all others that I have seen have suffered so much from pressure and from 

 loss or modification of the shell-substance that the evidence they afford of the original 

 conditions of the carapace is very obscure. A variety of E. minuta occurs also in the beds 

 between the Trias and the Lias (Rhsetic) of England and Scotland ; and carapaces of this 

 variety occur in excellent preservation in some localities (PI. II, figs. 9 — 15). 



To understand rightly the exact relationship of the Triassic and Rhoetic Estheria of 

 Britain to Estheria minuta of the Trias of the Continent, we must first take the latter in 

 hand, and work out its characters, geological position, and bibliography. 



The chief specimens of the German Estheria minuta that I have examined have come 

 from the south-western portion of the Triassic area of Baden, Wurtemberg, and Bavaria, 

 through the kindness of P. von Alberti, Sandberger, Bronn, Krantz, Hassencamp, and 

 others. From the Thuringian and Hanoverian Triassic areas, in some parts of which 

 E. minuta has been described as occurring abundantly, I have only one (Thuringian) 

 specimen. Of French specimens, from the Trias of the Vosges (Alsace), I have some from 

 Soultz-les-Bains, communicated by Dr. Schimper. 



My German specimens are — 



1 Resembling in general appearance several of the recent Estheria;, — such as those figured in pi, 1 1 

 (Jnnulosa) of the ' Proc. Zool. Soc.,' 1849. 



2 Viry similar to that of the recent E. Dahnlacensis, Durckh., from the freshwater marshes of the 

 Island of Dahalac, Abyssinia. (Baird, ' Proc. Zool. Soc.,' 1849, p. 89, Annulosa, pi. 17, fig. 2.) 



