104 BRITISH PALAEOZOIC PHYLLOCARIDA. 



? Dithteocakis Colei, J. Armstrong, 1871. Trans. Geol. Soc. Glasgow, vol. iii, 



Appendix, p. 29 ; and 1876, Catal. 

 W.-Scot. Foss., p. 45. 



— — H. Woodward, 1877. Catal. Brit. Foss. Crust., p. 72. 



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



— E., W., and J., 1887. Rep. Brit. Assoc, for 1S86 (1887), 



p. 63. 



— — Etheridge, 1888. Foss. Brit., vol. i, Pala?oz., p. 238. 



Specific Characters. — A relatively large oval-oblong carapace (laid out flat in 

 PL XXIV, fig. 2; halved in PL XXIII, fig. 1), with strong features of rugose 

 dorsal and mesolateral ridges, weak juxtadorsals, ventral fringe (especially 

 posteriorly), and posterior spines (two ventral and one dorsal). Delicate super- 

 ficial ornament reticulate and subaculeate. Dorsal junction of the carapace- 

 moieties surmounted by a serrated crest, with narrow side-flanges. In the 

 separate half (PL XXIII, fig. 1) this cristate ridge, remaining prominent, shows 

 its side-view. 



All the specimens referred to above (excepting PL XXII, fig. 7) formed part 

 of the original Irish series collected and described by General Portlock in 1843. 



PL XXIII, fig. 1. Mus. Pract. Geol., 6262. 'Catal. M. P. G. Fossils,' 1865, 

 p. 116. 



Size. — Moiety of valve 75 mm. long, 41 mm. wide. The whole carapace was 

 probably about 82 mm. wide. 



Characters. — This is a right valve, showing (1) a broad ventral margin, 

 dwindling away forwards, from which the fringe has been broken away ; (2) the 

 rugose mesolateral ridge ; (3) the almost straight posterior edge ; and (4) a pos- 

 terior portion of the dorsal rugose ridge, terminating in the postero-dorsal spine. 

 This ridge is rather too regular and too delicate in the drawing ; only the rough 

 ends of the chevrons come to the surface. 



Overlapping the antero-dorsal (upper in the figure) region of this valve is the 

 postero- ventral portion of another right valve, fig. 4 of PL XXIV. 



In a black shale, micaceous and calcareous ; being almost wholly composed of 

 compressed small Ostracods. In a similar shale (some with less of the small 

 Ostracods) are the specimens PL XXIII, figs. 2, 3, 4 ; PL XXIV, figs. 2, 4 ; and 

 PL XXVII, fig. 5. 



PL XXIII, figs. 2, 3, 4. (Tail-pieces.) Mus. Pract. Geol., Fig. 2, §&, 6261 ; 

 Fig. 3, ^, 6261 ; Fig. 4, \&, 6265. 



Size. — Fig. 2. Length 80 mm. Exposed segments 35 mm. ; penultimate 

 10 mm. ; ultimate 25 mm. Style 37 mm. Stylets 39 mm. 



