DITHYROCARIS COLEI. 167 



coated or replaced the test. Wherever this permits the original surface to assert 

 its presence, it is seen to be profusely spotted with minute triangular tubercles, or 

 obsolete prickles ; their angles pointing backwards. 



General Portlock remarked, at page 315, op. clt., withregai'd to the shape that, 

 " As a further means of distinguishing the species, the position of the lateral lines 

 may be noted, and the following dimensions taken into account : 



Length of buckler of lai-ge specimen . . 3'5 inches. 



Total breadth of buckler . . .2-6 ,, 



Breadth of single valve . . . 1'3 ,, 



The lateral line is nearer to the margin than to the axis, though with some 

 variation ; if, therefore, it be prolonged through the valve and considered a 

 chord, the length would be 3"1 inches, and the versed sine or perpendicular from 

 that line to the margin, -7 inch, or less than one-fourth of the chord." 



General Portlock's specimens, all belonging to the Lower Carboniferous 

 Series, came from the Tyrone Shales at Clogher, and the Derry Shales at 

 Ballynascreeu ; and Sir R. Griffith referred D. Golei to a Lower Carboniferous 

 Shale in the Yellow-Sandstone group at Auchmaclogh, Clogher, co. Tyrone. 



In 1863 Professor (now Sir Frederick) M'Coy described some specimens of 

 D. Colel from Auchmaclogh, Clogher, Tyrone, which were in the Griffith Collection 

 (Dublin). The Trustees of that Collection have kindly sent us two plaster casts 

 of the original specimens. One of them bears also the impression of a trifid tail, 

 like those in PL XXIII, figs. 2—4. 



In his 'Synopsis Carb. Fossils Ireland,' M'Coy thus described the species at 

 page 163 (without figures) : 



" Sp. Ch. — Longitudinally oval ; anterior eud mirrow, having a shallow rounded sinus in front, 

 posterior end broader ; margins sigmoidally curved, forming an acute sinus towards the centre ; sides 

 terminating in acute, angular, flattened spines ; the mesial [dorsal] ridge strongly orenated ; lateral 

 ridges almost as large as the mesial one, and similarly crenated ; short, sigmoidal, anterior ones also 

 similar; margins ot the valves obliquely striated ; surface otherwise perfectly smooth. 



"This large species is very closely allied to the Argas tricornis, Seouler. Taking one half of the 

 shield, or one valve, its length is about twice and a half the width. Length of single valves three 

 inches seven lines, width one inch six lines." 



PI. XXII, fig. 7. Mus. Geol. Surv. Scotland, m 4271', F f. No. 21. 



Characters and Size. — This is a filmy black remnant of a left valve, 43 mm. long 

 (formerly about 45 mm.) and 18 mm. wide. The fringed ventral margin and its 

 posterior spine, the mesolateral rugose ridge, the indications of the posterior 

 edge, and the spine terminating the dorsal margin are present. 



These features are very like those of D. Colei (compare PL XXIII, fig. 1 ; 

 XXIV, fig. 4), and we regard this Scotch specimen as a small representative of 



