172 BRITISH PALAZOZOIC FOSSILS. [CrusTacra. 
On comparison with Swedish specimens of the J. crassicauda of Dalman, I find the present species 
differs in the greater length of the head in proportion to its width; the cheeks also of I. crassicauda are 
wider than the glabella, while they are much less wide in the present species; the caudal shield is also 
considerably wider in proportion to the length in the Gothland trilobite, and the axal lobe of the thorax 
is one-fourth wider than the pleurze. 
Position and Locality—Abundant in the calcareous schists of Rhiwlas, N. of Bala Lake, Merioneth- 
shire; Llwyn y Ci, N. W. of Bala Lake, Merionethshire; Llanwddyn, E. of the Berwyn Mountains; Pont 
y Glyn, Diffwys, W. of Corwen. 
Explanation of Figures.—P1. 1. G. fig. 86. Perfect specimen, natural size, from Rhiwlas (the example 
figured belongs to the cabinet of Mr Davis.) 
ILLzanus Latus (Af°Coy). Pl. 1.E. fig. 17. 
Ref.—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. 1V. 
Sp. Ch.— Cephalic shield more than twice as wide as long, moderately gibbous towards the base, but 
about half of the front arched over to a vertical position (or at right angles to the basal portion or plane 
of the body); axal furrows considerably less than half the length of the head, width of the included space 
or glabella equal to two-thirds the length of the head; eyes small, near the lateral angles, their own length 
in front of the posterior margin, two-thirds the width of the glabella distant from the axal furrows. Length 
of head ten lines, width one inch nine lines. 
This is only likely to be confounded with the J. crassicauda (Dal.), from Gothland specimens of which 
it differs by the greater width of the head and less depth of the deflected front, and most remarkably, by 
the very small size of the cheeks, resulting from the eyes being removed almost to the lateral angles—in 
the J. crassicauda they are only half the width of the glabella distant from the axal furrow, and the portions 
of the cheeks from the eyes to the lateral angles is nearly one-third more than from the eye to the axal- 
furrows, while in the present species the cheek beyond the eye is little more than half the width of from 
them to the side of the glabella. Heads of the Dysplanus centrotus (Dal. Sp. =1. Bowmani Salt.) differ in 
their much greater proportionate length. 
Position and Locality—In the limestone of Wrae Quarry, Upper Tweed, near Broughton, S. W. of 
Peebles. A young specimen of the head, possibly of this species, little more than one line long, and with 
a front not quite so much deflected, and the glabella slightly longer and narrower, has occurred in the 
schistose ‘‘ Chazy limestone” of Knockdollian, three miles from Ballintrae. 
Explanation of Figures.—P\. 1. E. fig. 17. Head, natural size, from the limestone of Wrae Quarry. 
—Fig. 17 a. Profile of ditto. 
Ittainus Rosenperet (Kich.) Pl. 1. G. fig. 83 to 35. 
Ref. and Syn.—Cryptonymus id. Kichwald per Ingriam, &e. t. 3. f. 3.=Lllenus Murchisoni Salter, 
Mem. Geol. Surv. 
Sp. Ch.—Cephalic shield semielliptical, front narrow, much inflated, and curved inwards towards the 
margin ; axal furrows slightly sigmoidal, about half the length of the unbent part of the head, rather nearer 
to each other in front than at base, width of the enclosed space equal to the length of the furrows; eyes 
scarcely their own length from the posterior margin, and about half the width of the glabella from the axal 
furrows: thorax about as long as the unbent portion of the head, of ten very broad flat segments; axis twice 
the width of the pleuree, which are square at their extremities, abruptly deflected at right angles from the 
knee, which is tumid, close to the axis in front, and about one-fourth the width of the pleurce from it towards the 
tail; the anterior pleurze are directed backwards, tie posterior ones a little forwards, and the middle ones are 
slightly narrowed at the ends and extend at right angles to the axis; pygidiwm larger than the head, semi- 
elliptical, its length slightly exceeding the width, moderately convex, most so in the middle, axal furrows 
short, obtuse, parallel: entire surface, in some states of preservation, marked with minute flexuous striz 
