168 BRITISH PALAEOZOIC PHYLLOCARIDA. 



the large Irish D. Oolei, although the latter measures SO X 45 mm. in contrast 

 with 45 X 18 mm. 



In dark grey micaceous calcareous shale, containing some obscure small 

 Ostracods. From the Cement-stone Group, Tweeden Burn, 250 yards above its 

 mouth, near New Castleton, Roxburghshire. 



Another specimen, also from Tweeden Burn (F ^, No. 18, Mus. Geol. Surv. 

 Scotland), is also T). Colei, similar to PL XXII, fig. 7, but a fragment of a larger 

 carapace crushed flat. Remaining fragments of ridge and ventral edge, each 45 mm. 

 long. The distance between dorsal and mesolateral ridges 20 mm. 



PL XXVII, fig. 5. Mus. Pract. Geol., 6260, Derry, Sheet 40, 13. 



Size. — This is a fragmentary left-hand moiety ; length 40 mm., width 18 mm. ; 

 both measurements being imperfect. 



Character.- — This imperfect half-carapace has the characteristics of a small 

 Dithyrocaris Colei, and is almost exactly like the specimen shown in PL XXII, 

 fig. 7. It is evidently one of the original specimens collected by the Geological 

 Surveyors in Ireland, and described by General Portlock. 



In both PL XXII, fig. 7, and PL XXVII, fig. 5, the posterior edge is well 

 defined for half of its length as a narrow flat band, tapering slowly from the 

 postero-ventral spine to the place of the dorso-medial spine. 



0. Dithyrocaris orbicularis, Portlock, 1843. Plate XXIV, fig. 3. Mus. Pract. 



Geol., 6266. 



Dithyrocaris orbicularis, Portlock, 1843. Keport on the Geology of London- 

 derry, &c, p. 316 (not figured). 



— Morris, 1843. Catal. Brit. Foss., p. 73. 



— — Bronn, 1848. Index Palseont., vol. i, p. 135. 



Morris, 1854. Catal. Brit. Foss., edit. 2, p. 107. 



— — M'Coy, 1863. Synops. Char. Carb. Fossils Ireland, 



p. 163. 



— H. Woodward, 1877. Catal. Brit. Foss. Crust., p. 63. 



— — Bigsby, 1878. Thesaur. Dev.-Carb., p. 249. 



— E., W., and J., 1887. Kep. Brit. 'Assoc, for 1886, 



p. 64. 



— — Etheridge, 1888. Foss. Brit., vol. i, Pal., p. 238. 



Size. — Length of carapace 18 mm. ; width of carapace 24 mm. — approxi- 

 mately. 



