174 Mr. T. R. Jones on Beyrichise. 



the Harnage rock already frequently referred to. For the most 

 part, they much more nearly approach B. simplex than B. stran- 

 gulata, — their only other ally. If fig. 22 — one from amongst 

 this crowd of minute individuals in the Harnage rock (and 

 which, like others of the Simplices, have been hitherto regarded 

 as Cytherin(E) — be placed in the same category with figs. 26 and 

 27, we can but see what a difierence of form these little asso- 

 ciates present. 



Probably in mere casts of the external coverings of such mi- 

 nute animals, and with such general simplicity of outward form, 

 we should not expect to arrive at exact specific determinations. 



12. Beyrichia mundula, Jones. PI. VI. figs. 28-31. 



Annals and Mag, Nat. Hist. Ser. 2. No. 92 (Aug. 1855), p. 90. 

 pi. 5. fig. 23. 



Since writing the description of this Scandinavian species 

 (loc, cit.), I have met with several very well-preserved specimens 

 in the limestone No. 5 {vide supra, p. 84), some of which ex- 

 hibit the well-marked marginal rim and striato-punctate surface 

 (fig. 29 b). The generality of the individuals have a marked 

 straightness of the hinge-line (about two-thirds the length of the 

 valve), and a decided obliquity of the upper part of the margins 

 of the extremities, and frequently a conspicuous angularity of 

 the extremities themselves. In the specimens which have these 

 characters most strongly marked, the valves have a tendency to 

 be depressed towards their margins, and to lose the impression 

 of the dorsal sulcus (figs. 30 & 31) ; thus resembling the cara- 

 pace-valves of Leper ditia, — a genus which 1 hope to treat of in 

 my next notice of the Palaeozoic Bivalved Entomostraca. 



In the subjoined Table I have arranged the Beyrichia so as 

 to indicate the geological distribution of the genus and its three 

 subdivisions, as far as the species above described will permit. 

 The few other species known in the United States, already re- 

 ferred to (p. 168), and the Beyrichia collected by M. Barrande 

 and now to be seen in the British Museum, are all the species 

 of which I am cognizant, with the exception of some Lower 

 Silurian specimens of the Simplex group from Canada, which 

 have been collected by Mr. W. E. Logan, and will, I trust, form 

 part of the materials for a future notice on the Palaeozoic Bivalved 

 Ent?omostraca of Canada. 



