﻿PELTOCARIS APTYCHOIDES. 



113 



This Phyllopod has a discoidal, round or oval, tripartite shield, with a straight 

 median dorsal suture, and a curved nuchal suture, which, giving way after death 

 more easily than the other, has left in some instances a rounded, elliptical, or 

 semi-oval cephalic notch in the shield. The separate lateral pieces of the test, 

 instead of a straight sloping inner edge as in Apt ij chop sis, have an inner concave 

 curve meeting the convexity of the outer margin. These two lateral moieties, 

 however, are not so frequently found separate as is the case with Aptychopsis. 

 In some instances a smaller notch appears at the bottom or apex of the curved 

 notch, sometimes with a little escutcheon peculiar to it. The shield is smooth in 

 all the specimens here figured. A very dubious indication of concentric striation 

 is traceable in fig. 8. 



One allied specimen has been figured and described (' Quart. Journ. Geol. 

 Soc.,' vol. xxii, 1866, p. 504, pi. xxv, fig. 6) which has concentric lines of growth. 

 As it represents a different species, we dedicate it to its discoverer, W. Carruthers, 

 Esq., F.R.S. ; see page 116. 



1. Pbltocaeis aptychoides, Salter, 1852 and 1863. Plate XVI, figs. 1 — 3 and 9. 



Dithyrocaris apttchoides, Salter. Quart. Journ. Geol. Soc, vol. viii, 1852, 



p. 391, pi. xxi, fig. 10. 

 Ceeatiocabis aptychoides, Salter. Ann. Mag. Nat. Hist., ser. 3, vol. v, 1860, 



p. 161. 



Peltocaris aptychoides, Salter. Quart. Journ. Geol. Soc, vol. xix, 1863, p. 88, 



fig. 1 ; p. 90, fig. 4. 

 — Bigsby. Thesaur. Silur., 1868, p. 76. 



— — H. Woodward. Catal. Brit. Foss. Crust., 1877, p. 77. 



— — T. B. J. and R. W. Geol. Mag., 1884, p. 355. 



— — — Eeport Brit. Assoc for 1884 



(1885), p. 92. 



— — Etheridrje. Foss. Brit., vol. i, Palseoz., 1888, p. 62. 



Mr. Salter, treating of this species, describes and figures a smooth, flat, round, 

 tripartite test, with a nuchal or rostral notch as broad as long, and of a parabolic 

 shape, with a depth of about one-third of the whole length of the test. The 

 umbonal angles at the inner end, or apex, of the notch are often isolated by short 

 curved sutures (fig. 1, 1863), and sometimes lost on account of that sutural 

 division (fig. 10, 1852). His fig. 1 has a round outline (restored ?) measuring 

 13 mm. each way, and the notch is 4 mm. deep and broad. His fig. 10 shows 

 two valves united, slightly distorted by pressure, and indicating an oblately 



15 



