THE 



GEOLOGICAL MAGAZINE, 



NEW SERIES. DECADE II. VOL. Vlli. 



No. VIII.— AUGUST, 1881. 



os-ia-insT-A-Xi -a.i?,tigxjES. 



I. — Notes on some Paleozoic Bivalved Entomostraca. 



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



(PLATES IX. AND X.i) 



1, Cypridina? Plate IX. Figs. 7a, 7b. 



Length, ^ inch. 



THE specimen here figured is an internal cast of a right valve, 

 occurring in the well-known, reddish, fossiliferous, PalcBOzoic 

 quartzite of the Triassic pebble-bed at Budleigh-Salterton, in Devon- 

 shire ; and it resembles some forms of Cypridina hrevimentum, J. 

 and K. (" Monogr. Carbonif. Entom." Pal. Soc. 1874, p. 15, pi. 5, 

 figs. 15-19), in general aspect; and also in some respects Polycope 

 simplex, J. and K. (op. cit. p. 54, pi. 2, fig. 12). It was detected by 

 the late Mr. J. W. Salter (in 1865 ?) during his enthusiastic study 

 of that interesting conglomerate. 



Mr. T. Davidson has brought together all that is known of this 

 old pebble-bed of Devonshire, in his " Monograph of the Fossil 

 Brachiopoda," Pal. Soc, Supplem. Part IV. 1881; and has therein 

 and elsewhere added greatly to our knowledge of its palseontology, 

 and of its geological relationships. Both Silurian and Devonian 

 fossils are known to occur in the pebbles referred to ; and, as far 

 as appearances serve, the unique specimen under consideration is 

 a Carboniferous form. We cannot say, however, that it may not 

 have been Devonian, or even Silurian ; for Bivalved Entomostraca 

 of existing genera are represented by valves similar to their own 

 (and valves are our only evidences) in various Palaeozoic strata. The 

 matrix is decidedly that of the other old pebbles of the conglomerate ; 

 and it would have been very strange if all and each of the three great 

 formations should have given a similar quartzite to one pebble-bed. 



Being only an internal cast in granular quartzite, with a portion 

 of the margin (postero-ventral) still imbedded in the matrix, it fails 

 to show any very distinct features, beyond an oval outline, with a 

 broad, shallow, oblique, anterior antennal notch (scarcely making a 

 beak), and with a moderate convexity of the valve, greater in front 

 than behind. 



If the want of prominence in the beak, owing to the obsolete con- 

 dition of the notch or sinus, separates this form from Cypridina, and 

 yet, if the prominence remains too strong for Polycope, we shall have 



1 These two Plates have been drawn with aid of a Grant from the Eoyal Society 

 for the illustration of the fossU Bivalved Entomostraca. 



DECADE II. — VOL. VIII. — NO. VIII. 22 



