120 BRITISH PALEOZOIC PHYLLOCARIDA. 



DisciNocABis Bbowniaha, Armstrong, Young, and Bohertson. Catal. West-Scot. 



Foss., 1876, p. 7. 



— _ Bigshy. Thesaur. Silur., 1868, p. 74. 



— — Lapworth and Swanston. Proceed. Belfast Nat. Field 



Club, Appendix, 1S77, p. 114, and Table, pi. vii, 

 figs. 24 a, 25 a, and 25 c. 



— — H. N. and E. Catal. Cambr. Sil. Foss. Pract. Geol. 



Mu9., 1878, p. 28. 



— — T.R. J. and R. W. Geol. Mag., 1884, pp. 348 and 



— — — 351. Keport Brit. Assoc, 



1884 (1885), pp. 75 and 78. 



— — Etheridge. Foss. Brit., vol. i, Palaeoz., 1888, p. 51. 



This is a circular shield-like test, closely resembling a Discina at first sight, 

 but it has a section of one-sixth of its arc removed in nearly every specimen. 

 This triangular anterior or nuchal valvular piece is crossed by concentric strige 

 coincident with the lines of growth on the rest of the test. The rostral notch has 

 normally an angle of about 90°. It extends less than half the length of the shield. 



The shape of these little fossils has been much modified by pressure— vertical, 

 lateral, or oblique. In fig. 12 the shell seems to have retained its original shape ; 

 others have been widened by pressure, as figs. 15, 16, 22, and especially fig. 17 ; 

 some have been obliquely squeezed, as figs. 21 and 23 ; and some have been 

 narrowed by cross-pressure, as figs. 13, 14, and especially figs. 18 and 19. 



A larger specimen, and apparently with the two lateral flaps or valves folded 

 together, was figured in the ' Quart. Journ. Geol. Soc.,' vol. xxii, 1866, pi. 25, 

 fig. 5, and described at page 503 as retaining some remains of the tail-segments 

 with the folded shell. Unfortunately the specimen (formerly in Mr. D. J. Brown's 

 cabinet) has been lent or given away, at all events lost, and we cannot at present 

 learn anything more about it. 



PI. XVI, fig. 12. Black shining film on black graptolitic, finely micaceous 

 shale. The test is almost circular and nearly perfect, but the nuchal piece is 

 somewhat obscure, having been broken or slightly shifted, so as to leave a small 

 open angle at the upper part of the left-hand slope of the notch. The width of 

 the shield to the length is as 12 to 11. 



From the Moffat shales of Dumfriesshire. Coll. Carruthers. British Museum. 

 No. 58869. This is probably the specimen represented by fig. 7 (somewhat 

 restored), ' Quart. Journ. Geol. Soc.,' 1866, pi. 25. 



PI. XVI, fig. 13. Black film on black shale from Garple Linn. It is slightly 

 deformed by cross-pressure. Mus. Geol. Surv. Scotland. M. 4371. 



PL XVI, fig. 14. Black film on black shale from Dobbs Linn. Deformed by 

 pressure. Mus. Geol. Surv. Scotland. M. 4439 c. 



PL XVI, fig. 15. A rather large specimen, but broken and widened by vertical 



