DITHYROCARIS COLEI. 163 



accordingly. It is smaller than the type-form, and its carapace must have been 

 rather oval, like figs. 1 and 2, PI. XXX, and not so orbicular as fig. 3. 



Figs. 8 a, b, c. Leeds Mus. Coll., No. 43. 



An imperfect posterior half of a left valve (about 14 mm. wide), showing the 

 wide ventral border (as in PI. XXX, fig. 3), with the mesolateral, juxtadorsal, and 

 dorsal ridges very distinct. The juxtadorsal is oblique (as also in fig. 9). The 

 left-hand edge of the dorsal ridge seems to have been squeezed in under the 

 neighbouring part of the test. The postero-ventral spine is long and sharp ; the 

 medio-dorsal spine is much shorter. 



The ornament of lines and network in fig. 8 b extends over the dorsal ridge 

 and the test in its vicinity ; the pattern of linear chevrons pointing downwards 

 (backwards) passes sideways into the general reticulation. The parallel sinuous 

 lines on one side of the limit of the dorsal ridge differ, but not essentially, from 

 those on the left-hand side of that limit. The irregular meshes are punctate 

 (fig. 8 c). 



PI. XXXI, fig. 9. Leeds Mus. Coll., No. 40. 



Size. — Valve, length about 35 mm. probably when perfect; width 15 mm. 



Characters. — Rather more than half of the left moiety of a carapace ; imperfect 

 at the front end. Besides the ventral border, partly fringed, the mesolateral, 

 juxtadorsal, dorsal, and the right-hand juxtadorsal are distinct. The two juxta- 

 dorsals are set obliquely (see also fig. 8 a), and thus appear to be in their normal 

 position and not squeezed out of place. They are parallel one to the other. 



The gastric ridge on the left side, and the nuchal ridges on both valves, are all 

 apparent. 



8. Dithtrocaeis Colei, Portlocl; 1843. Plate XXII, fig. 7; Plate XXIII, figs. 1—4 ; 



Plate XXIV, figs. 2, 4; Plate XXV, 

 figs. 9 a, b, c (?) ; Plate XXVII, fig. 5. 



Dithyeocabis Colei, Portlock, 1843. Report Geol. Londonderry, &c, pp. 314, 



565, 570, pi. xii. 



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



— — M'Coy, 1844. Synops. Char. Carb. Foss. Ireland, p. 163. 



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



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



— — R. Griffith, 1862. Journ. Geol. Soc. Dublin, vol. ix, p. 48. 



— — M'Coy, 1862. Synops. Char. Carb. Foss. Ireland, edit. 2, 



p. 224. 

 ? — — J. Young, 1868. Trans. Geol. Soc. Glasgow, vol. i, p. 58. 



