180 BRITISH PALEOZOIC PHYLLOCARIDA. 



smooth, baviug probably lost the thin external ornamented coat. Ventral margin 

 depressed and apparently simple (but other specimens show that it turned in at 

 the edge). Dorsal margin quite simple and straight as far as it is preserved. 

 Along the middle of the valve is a raised ridge (mesolateral) without visible rugas. 

 At its front end it curves gently towards the antero-dorsal corner of the valve, 

 and almost touches the middle of the somewhat sigmoidal cephalic ridge. Near 

 and parallel to the middle part of the dorsal margin is a thin ridge (juxta- 

 dorsal), disappearing forward among some feeble elevations accompanying a 

 faint nuchal ridge. In grey Carboniferous Limestone from Vise, Belgium. 



Variety (?). — Mounted with the foregoing there is a smaller specimen of a left 

 valve of the same species, also from Vise (in cream-coloured limestone, with a 

 small Gasteropod and other little fossils). This presents the same features as fig. 

 8, but differs in size and proportions ; its ventral edge is more broadly depressed, 

 and its median convexity is proportionally greater. 



Size. — Length 13 mm. ; breadth 7 mm. 



PI. XXI, fig. 9. Brit. Mus., No. 44987, No. 24. 



Size. — Length of valve, imperfect, about 30 mm. ; breadth of valve about 12 

 mm. 



Characters. — A left valve, similar in general features to fig. 8, but not so 

 obliquely rounded in front ; imperfect behind. The little cephalic ridge ends 

 behind in a small smooth knob. The surface is ornamented with numerous, 

 delicate, closely-set strise, curving round the front part of the valve, parallel with 

 its border, and passing along the ventral region. The thin ridge near the dorsal 

 border dies away forwards among numerous, small, sinuous strias, irregularly 

 parallel, and passing away backwards into the longitudinal strias of the dorsal 

 region, which are not very distinct in this specimen. 



A part of a smaller valve is attached to this little piece of limestone. 



This specimen (fig. 9) has been described and figured in the ' Geol. Mag.,' vol. 

 viii, 1871, p. 106, pi. iii, fig. 4. It is from the Carboniferous Limestone of Settle, 

 West Yorkshire. Collected by the late Mr. J. H. Burrow. 



PI. XXI, figs. 11 a—f. Mus. Univ. Cambridge. 



Size. — Length of valve, imperfect, 35 mm., probably 39 mm. when perfect; 

 breadth of valve 15 mm. 



Characters. — This is a right valve, presenting the characteristic features of 

 fig. 8, but slightly broader, and with more distinct ornament of the surface. 

 Near the ventral margin the strise are simple, though divergent (fig. 11 d) ; along 

 the mesolateral ridge they run up on both sides and coincide with the angular 

 lines of obscure chevrons (fig. 11 e ; better seen in another specimen, not figured), 



