174 BRITISH PALEOZOIC PHYLLOCARIDA. 



cephalic ridge with its little crater-like end, and some protuberances near by, lie 

 between the nuchal ridge and the remaining anterior end of the mesolateral 

 rugose ridge of this right-hand valve. 



The surface is minutely reticulate, and frequent trigonal outgrowths of the 

 meshes form obscure or abortive prickles (figs. 5 b, d, e). The dorsal crest is 

 very prominent (compare PI. XXIII, fig. 1), showing both of its sides (figs, ba, 

 b, c, (I). Its chevron-like and imbricated ruga? rise out of its reticulate sides, one 

 of which is shown in the fig. 5 d. Clearly marked off from the rest of the 

 surface is one flange of the overriding crest, as in PL XXIV, fig. 1, and PI. XX, 

 figs. 1 a, 2 a, b, 3 a and g. In the arrangement of the ridges (cephalic and others) 

 and in its subaculeate ornament this specimen closely resembles I), tricornis 

 (PI. XXIV, fig. 1) ; also in its reticulation, which is well preserved. 



Two counterparts in a split calcareous nodule ; from the shales of the Redes- 

 dale Ironstone of the Lower Carboniferous series, Northumberland. Collected by 

 Mr. Dunn. 



PL XXIV, figs, ba, b; PL XXII, fig. 4 (magnified part). Mus. Geol. Surv. 

 ScotL, F ^, No. 9. 



Size. — Length 13 mm., breadth 10 mm., depth or thickness 4 mm. 



Characters. — A small specimen referable to D. tricornis. It exhibits three 

 obscurely rugose ridges (one dorsal and two mesolateral) along the surface, and 

 two cephalic ridges in front. Some distortion from pressure has narrowed the 

 right moiety, and made its mesial ridge oblique to its ventral border and to the 

 dorsal ridge. The end view (fig. 5 b) shows a subquadrate outline, with sloping 

 sides, which are the down-folded and inturned lateral expansions of the ventral 

 margins outside the mesolateral ridges. 



PL XXII, fig. 4, exhibits a magnified view of a part of the surface of fig. 5 a, 

 comprising the right cephalic ridge and its crater-like ocular spot, and the front 

 end of the right mesolateral ridge, formed, like the other ridges, of imbricating 

 chevrons. The coarse (worn ?) reticulation is also shown, and the irregularly 

 scattered tubercles or false prickles. 



This interesting little fossil has been referred to and figured in the ' Geol. 

 Mag.,' vol. x, p. 485 ; and dec. 2, vol. i, p. Ill, pi. v, fig. 7. 



In black calcareous shale. From the Lower Limestone group, Kirktonholme 

 Cement Works, East Kilbride. Mr. A. Patton Coll. 



PL XXVII, figs. 4 a— e. Neilson Coll., F. 



Size. — Length of carapace 17 mm., breadth 13 mm., depth 5 mm. 



Characters. — A small individual like D. tricornis, of a neat suboval shape, and 



