Prof. T. Rtqjert Jones — On Silurian Entomostraca. 511 



IV. — Notes on some Silurian Entomostraca from Peeblesshire.' 

 By Professor T. Rupert Jones, F.R.S., F.G.S. 



SOME specimens of dark olive-grey mudstone from Peeblesshire, 

 collected aud shown to me by Mr. D. J. Brown, contain several 

 internal and external casts of small bivalved Entomostraca. 



Fig. 1. Bairdia ? Broivniana, right valve. 

 2a. Beyrichia impendens ; left valve. 

 2b. B. impendens, var. tuberosa ; right valve. 

 3. Primitia protenta ; right ? valve. 

 4ff. Entomis aciciilata ; right valve. 

 45. E. aciculata ; riglit valve, crushed. 

 (All magnified about sis diameters.) 



1. Bairdia ? Browniana, Jones, 1871, MS. [Fig. 1.] — Two internal 

 casts; fusiform, with one margin [dorsal?] more convex and more 

 sinuate than the other, and with one end much more acute than the 

 other, which is narrow and neatly rounded. Length of valve, -j-Vth- 

 inch ; breadth or height, -^-Lth inch. 



This small and somewhat obscure form most nearly conforms in 

 shape with some of the elongate subtriangular fossil " Bairdies," 

 such as B. siliqua, Jones, and some of the recent Macrocypridoe, etc. 

 In its size, however, and (as far as can be seen in the casts) in its 

 shape and proportions, it differs from all the other forms ; it may, 

 therefoi'e, be catalogued as Bairdia ? Browniana, taking its name from 

 its discoverer. The very minute, elongate, Silurian Cythere Grind- 

 rodiana (Annals Nat. Hist. ser. 4, vol. iii. p. 212, fig. 1) is readily 

 distinguished from this Bairdia-like species. 



2. Beyrichia impendens, Jones, 1869, " On the Palaeozoic Bivalved 

 Entomostraca," Proceed. Geol. Assoc. 1869, p. 11, figs. 4a, 4&, 

 [Pigs. 2a. 26.] 



This variable little Beyrichia is represented among Mr. Brown's 

 specimens from Peeblesshire by casts of several individuals, in which 

 the dorsal furrow is variously developed (and altered by crush), as 

 well as its associated tubercle. In some specimens one side (hinder) 

 of the furrow is so much elevated as to form an additional though 

 small tubercle, making an unequal pair with the other or usual 

 tubercle in the bosom or anterior curve of the furrow; thus ap- 



^ ' Reprinted, with woodcut added, and correction, by permission, from the " Trans- 

 actions of the Geol. Soc. Edinburgh," vol. iii. part 2, 1874. 



