156 BRITISH PALAEOZOIC PHYLLOCARIDA. 



Specific Characters.— We have not seen the original specimen of D. Seoul eri, 

 nor are we quite certain that we have met with any specimen truly representing 

 that species. From the description and figure 1 published in the ' Synops. Char. 

 Carb. Foss. Ireland ' this species seems to have the following characters :— A 

 nearly round clypeiform test (36 mm. long, 34 mm. wide), slightly convex, with a 

 strong rugose dorsal ridge, two ocular or gastric ridges, and two rugose meso- 

 lateral ridges: otherwise smooth. A double ventral border is shown, with a 

 marginal fringe extending from the subtriangular frontal notch to the two strong 

 posterior spines ; between these the posterior border is almost straight. 



The last abdominal segment (or rather what represents its right-hand moiety), 

 14 mm. long, is ornamented with sinuous lines, passing obliquely backwards, from 

 the outer edges to the centre. At the end of this segment is a broad-headed 

 style (6 mm. wide), and a stylet on each side of it. The style, 25 mm. long in 

 the figure, is bayonet-shaped, with oblique fine strise on its sloping faces. The 

 stylets (each showing a length of 22 mm.) are blade-like and tapering (about 

 3 mm. broad near their articulation) and coarsely striate. 



The caudal spines indicate the dorsal aspect by their arrangement, the stylets 

 passing under and behind the top of the style; but the piece of test at the place 

 of the ultimate segment shows the oblique lines arranged as on the central surface. 

 See D. testudinea, PI. XXI, fig. 4. 



In his ' Synopsis of the Characters of the Carboniferous Limestone Fossils of 

 Ireland,' ~ 1844, Professor (now Sir Frederick) M'Coy refers at p. 163 to Dithy- 

 rocaris Scoideri, M'Coy (pi. xxiii, fig. 2), as follows : 



" The characteristic length of expanded pair of valves very slightly exceeding the width ; 

 surface smooth ; central and lateral ridges transversely wrinkled ; frontal notch as deep as wide, 

 rounded. Valves, when spread flat, forming a nearly orbicular shield, the length very slightly 

 exceeding the width, and having a deep rounded notch in front ; central ridge or hinge strong, 

 rounded, regularly marked with transverse wrinkles [PI. XXV, fig. 6 b] ; lateral ridges marked 

 with irregular, fiat, scale-like undulations [PI. XXV, fig. 6 c] ; intermediate short ridges nearly 

 straight, slightly bent towards the central ridge above and towards the lateral ridges below ; 

 surface smooth, margin of the valves narrow, fringed or obliquely striated, immediately within which, 

 on the lateral margins, is a plain rounded ridge, divided longitudinally by a nearly mesial sulcus ; it 

 is close to and parallel with the outer margin for about the upper half of its length, then gradually 

 turning in towards the lateral ridge, where it widens ; tail exactly equalling the body in length, 

 terminating as usual in three spines of nearly equal length, the central one triangular, marked with 

 very fine oblique stria?, meeting at an acute angle on the central ridge ; two lateral spines rounded, 

 coarsely sulcated longitudinally. Width of the expanded pair of valves one inch four lines; length to 

 tip of posterior spine one inch five lines ; length of central spine of tail one inch." 



1 This has been photographed from M'Coy's figure, and reproduced in PL XXV, figs. 6 a — c. 

 ,J Reprinted in 1862, with Table of Fossils and Localities. 



