Crustacea. | LOWER PALAZOZOIC ARTICULATA. 163 
with seven or eight narrow segments, sides slightly convex, with five flattened ribs, each divided by a fine 
mesial suleus. Average length of head four lines, of pygidium three lines 
This interesting species blends in some measure the characters of the subgenus Portlockia with those 
of Phacops proper. I have noticed that all the Portlockiw, though when perfect shewing but the basal 
pair of segmental furrows to the glabella, yet when decorticated shew faint and delicate traces of the other 
two pairs, never comparable in strength, however, to the basal pair. All the specimens of the present 
species are internal casts, therefore shewing the three sets of furrows, but the basal pair being so much 
stronger than the others favours the idea of its being a Portlockia, as no such difference exists in Phacops 
proper. The head and pygidium, here noted, have not been absolutely found in contact. 
Position and Locality—vVery common at Maes Meillion, Bala, Merionethshire; Glyn Ceiriog; Bryn 
Melyn, Bala, Merionethshire; S.W. of Pwllheli, Caernarvonshire; Rhiwargor, near Llanwddyn; Cowney 
River, Montgomeryshire ; Cefn Goch, Llansantfraid; schists of Hengurt Uchaf. 
Explanation of Figures.—P\. 1. G. fig. 17 and 18. Cephalic shields, natural size—Fig. 19. Pygidium 
natural size. 
PortLockia Stoxesi (MZ. Edw. Sp.) 
Ref. and Syn.—Asaphus macrophthalmus (Brong. pars. t. 1. fig. 5). Calymene id. Sil. Syst. t. 14. f. 2 
Sp. Ch.—Cephalic shield semicircular, twice as wide as long; g/abella subrhomboidal, clavate, the broad 
front slightly pomted in the middle, granulated; neck segment thick and strong, one strong segmental 
furrow on each side of the narrow base immediately above the neck-furrow, reaching nearly across (on 
casts of the inner surface I have seen traces of the other two segments as delicate impressed lines not 
visible on the external crust); cheeks tumid, small; eyes very large, reniform, coarsely reticulated ; lateral 
and posterior margins strongly defined, thickened, lateral angles obtusely rounded; pygidiwm nearly semi- 
circular, slightly more than twice as wide as long, axis of five segments, side lobes with about four fine 
segmental furrows; length of head about three lines. 
Position and Tiere —Wenlock Limestone of Dudley, Sess AEDs Llangynyw Rectory, Montgomery- 
shire; Garden Quarry, Aymestry, Herefordshire. 
Genus. CHASMOPS (M/°Coy). 
Ref.—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IV. 
Gen. Char.— Cephalic shield sub-semicircular, lateral angles produced backwards into triangular spines ; 
glabella very large, clavate, frontal portion very wide, transversely oval, only two distinct pairs of segmental 
lobes, the anterior pair very large, triangular, posterior pair small, middle pair entirely obsolete or reduced 
to minute tubercles; neck segment strong; cheeks small, triangular; eyes small, prominent, rounded, cor- 
responding in length to the middle portion of the first lateral lobes of the glabella; eye-line encircles 
the front of the glabella close to the margin, descends with an inward inclination to the eye, extending 
from behind the eye directly outwards to the lateral margin, which it cuts considerably in advance of the 
angle (thorax of eleven joints, jid. Hichwald); pygidium obtusely rounded, posterior margin deflected, 
anterior margin wider than the posterior, axis of about ten ribs, lateral ribs about two less, duplex. 
The Calymene Odini of Eichwald may be looked upon as the type of this genus. It differs from 
Calymene in the glabella being so much wider in front than at base, in the anterior lateral lobes being 
largest, in having but eleven(‘) body segments, and in its eye-line cutting the external margin in front 
of the produced angles; these differences become agreements when compared with Phacops, from which 
it differs in the size and shape of the eyes. Of these organs in the present genus, and in Calymene, 
nothing is known beyond that they were of so tender and delicate a nature as readily to fall out after 
death so as seldom or never to be found in the fossil state, their position being merely indicated by a 
hole, roughly filled by the matrix, forming the ‘‘hiant” eyes of systematists; in Phacops, on the con- 
trary, the cornea is of extraordinary strength and so firmly united to the rest of the cephalic shield, that 
no matter how much crushed the specimens may be the eye always remains, and from its constant 
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