APPENDIX. 121 



2. Beyrichia Pyrrh^, Eichwald, sp. PI. V, figs. 18, 19. 



CypEis Pyrrh^, Eichwald. (The name only is given in Jazykov's Table of the Formations 

 of the Government of Simbirsk, published by the Petersburg. Mineral. 

 Gesellschaft, 1844, according to Von Keyserling.) 



Cytherina PYBRHi5),i Eichwald. Geogn. Riissl.,2 1846, p. 466. Bullet. Soc. Imp. Nat. 

 Moscou, annee 1857, vol. xxx, 2nd part, 1857, p. 307. 



Bairdia Pyrrh^, Eichwald. Lethsea Rossica, 7th part, 1860, p. 1344, pi. 52, fig. 3 a, h. 



Length of the figured specimen, -^-^ inch.^ Height, -^ inch. 



Carapace-valves oblong-ovate ; extremities nearly equal, the posterior being rather 

 larger than the other ; upper margin straight, curved symmetrically at the ends ; dorsal 

 region faintly impressed by two short, shallow, transverse indentations, which obscurely 

 divide that part of the valve into three nearly equal parts. The anterior sulcus is the 

 more distinct of the two. A slight, neat, flattened border follows the curved margin of 

 the valve. The surface is beautifully reticulated with minute hexagonal pits (fig. 19). 



M. d'Eichwald correctly describes this Kttle fossil as follows, excepting that he 

 omits the ornamentation and the rim, and regards the faint dorsal elevation as due to the 

 internal attachment of the muscle : — " Testa exigua, tenuissima, plana, ovato-dilatata, 

 uno latere latiore altero, utroque rotundato, tuberculo sive eminentia musculari prope 

 marginem dorsalem obvia, foveolam utrinque prae se ferente, oculo non conspicuo." He 

 remarks that the anterior sulcus is more constant than the other, and that some indi- 

 viduals have a more rounded outline than others, and do not show the dorsal protu- 

 berance. In the figure given in the ' Lethsea Rossica ' the dorsal notches are more distinct 

 than they are in our specimen. 



This little Entomostracan has no family-relationship to the Cypridce, and least of all 

 to the sub-genus Bairdia in particular. Its general features and its dorsal notches show 

 it to be a Beyrichia, though with feeble characters of carapace. Indeed, we may have 

 ultimately, for convenience of grouping, to separate the simpler forms from those with 

 many-lobed carapaces, however gradual may be the stages of difierence. Eurther, the 

 species before us presents an interesting passage-form between the simple Beyrichia; and 

 the non-sulcated carapaces known as Cytheropses.'^ The amount of sulcation in B. Byrrhce 



1 Cythere Pyrrhce (?), Keyserling, in Schrenk's ' Reise,' &c., 1854, p. 112, pi. 4, fig. 41, is C. ovata, 

 Eichwald. See ' Bullet. Soc. Imp. Nat. Mosc.,' 1857, p. 308 ; and Eichwald's ' Leth. Rossr,' p. 1344. 



2 Published in the Russian language. 



3 M. d'Eichwald has described specimens having the dimensions of 1 by \\h line. 



* Compare Cytheropsis concinna(t), 'Annals Nat. Hist.,' April, 1857, p. 254, pi. 9, fig. 3. 



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