98 BRITISH PALAEOZOIC PHYLLOCARIDA. 



T. E. J. and H. W., ' Geol. Mag.,' 1884, pp. 349 and 354. 

 T. E. J. and H. W., ' Eeport Brit. Assoc' for 1884 (1885), p. 87. 

 T. E. J. and H. W., ' Monogr. Brit. Pal. Phyllop.,' pt. 1, 1888, p. 2. 

 Etheeidge, ' Poss. Brit.,' vol. i, Palseoz., 1888, p. 45. 



A circular or elliptical, slightly convex, tripartite shield or carapace ; divided 

 by a median " dorsal " suture extending from the posterior margin forward to 

 within half, or a third, or a fifth, of the length of the test, according to the shape 

 of the latter, and then meeting the apex of a symmetrical V-shaped suture, which 

 extends to the front margin at different angles in different species. This angular 

 ("nuchal") suture forms a line of much weaker resistance than the longitudinal 

 suture ; and the carapace has very frequently given way after the death of the 

 animal, and allowed the triangular ("rostral," "cephalic," or " complementary") 

 portion to be removed, together with the anterior limbs and soft parts of the 

 animal as suggested by Dr. H. Woodward.' Thus an angular notch is often 

 present in the forepart of the fossil carapace. The median suture has often been 

 pressed inwards, but sometimes it has parted, leaving the two larger parts of the 

 test separate. These remain as sub-triangular plates (the principal or lateral 

 parts), straight-edged and angular on the inner margin, and either elliptically 

 curved or almost semi-circular on the outer or free borders. They occur usually 

 as black carbonaceous films on the bed-planes of the strata ; but sometimes they 

 have a somewhat corneous or chitinous appearance. 



A concentric linear ornament covers the whole shield; numerous delicate 

 ridges and furrows, following the curve of the outer margin, are concentric to the 

 point where the dorsal and nuchal sutures meet in front of the centre of the test. 

 The style of ornament is similar to that of the bivalve Edheria, which shows a 

 neat arrangement of raised lines of growth, concentric with the umbones. In the 

 case of Ellijjsocaris, even the interlinear sculpturing is present (' Geol. Mag.,' Oct., 

 1882, p. 445). Delicate radiate striae, crossing the concentric lines, are sometimes 

 visible. If the two valves of Estheria be laid open, back to back, their surface 

 would represent the shield of Aptijchopsls ; the open angle then formed by their 

 anterior margins would be analogous to the nuchal notch ; and for that of their 

 hinder margins we may find an analogue in the split posterior border of Dij^tero- 

 caris and other forms allied to Aptychopsis. 



M. Barrande indicated the existence of this genus in his ' Parallele entre la 

 Boheme et la Scandinavie,' 1856, p. 62; here he also stated that Prof. Angelin 

 had found the same kind of fossil in Dalecarlia and Gothland in Upper Silurian 

 strata, at about the same horizon (Angelin's Regiones D et B in the former and 

 Regio E in the latter country) as that in which they occur in Bohemia (etage 

 calcaire inf^rieur E). See also ' Sil. Syst. Boheme,' vol. i; Suppl., p. 455. 



1 ' Quart. Journ. Geol. Soc.,' xxii, p. 504 ; and ' Geol. Mag.,' dec. 2, vol. is, 1882, p. 387. 



