152 BRITISH PALAZOZOIC FOSSILS. [Crusracea. 
4th Subfamily. PARADOXIN AE. 
Pleuree flat, horizontal, without facets, with a straight pleural groove, and terminating in spines inclining 
backwards. 
This subfamily is composed of a group of long-bodied Trilobites, having for the most part large cephalic 
shields, with the angles prolonged into spines, and very small flat caudal shields of few segments ; none of them, 
I believe, can roll into a ball; their pleurze are very wide and horizontal, not bent downwards at the ends, so 
that the body is flat ; they are destitute of facets, and have a long straight pleural groove extending their whole 
length, dividing each into two tumid portions, one or both of which are extended into long sharp spines, in- 
clining obliquely backwards. This latter character, of all the pleure terminating in separated spines, gives a 
peculiar physiognomy to the Trilobites of this group. The thoracic segments vary from eight to twenty-three 
in number ; 
The principal British Genera are, Ist, Paradowides (Olenus being regarded as a subgenus); 2nd, Aci- 
daspis ; 3rd, Staurocephalus ; 4th, Ceraurus; 5th, Eccoptochile ; 6th, Spherexochus ; 7th, Zethus. 
Genus. ACIDASPIS (Murch.) 
Syn.—Odontopleura (Emmerich.) 
Gen. Char.—Cephalic shield wider than long, subquadrate or semicircular, margin tumid, often spinous, 
lateral angles forming long slender spines; g/abella convex, narrow in front, not reaching the front margin, 
with two or three lateral lobes on each side, base prolonged backwards into one or two long thick spines; 
antennary pores usually distinct, close to the front of the glabella; eye-line tumid, cutting the margin on each 
side in front of the glabella, and extending from the eyes, which are very small, to the posterior margin rather 
nearer the angles than the glabella on each side; thoraa of eight joints, axis convex, narrow; pleure wide, 
perfectly flat, each with a nearly mesial pleural furrow parallel with the margin, the upper portion thickest, 
prolonged beyond the posterior, and terminating in a long spine deflected at a considerable angle backwards ; 
pygidium small, semicircular, axis very short, of two joints, sides flat with but one segmental furrow, ending 
in a long spine at the margin of each side, the rest of the margin with many smaller spines. 
Acrpaspis Brieutir (Murch.) 
Ref—Murch. Sil. Syst. t. 14. f. 15. 
Sp. Ch.—Cephalic shield convex, subsemicircular, front flattened, limb thick, rounded, denticulate at the 
sides, produced at the angles into long, slightly flexuous, obtusely rounded spines; g/abe/la convex, strongly defined, 
narrow and rounded in front, widening towards the base, each side with a pair of large spheroidal segmental 
tubercles, the posterior ones largest ; cheeks small, very tumid ; eyes situated near the base of the glabella; a 
narrow ridge extends from the eye on each side to the antennary punctures, which are large, on each side of 
the front of the glabella; neck-segment prolonged horizontally backwards into an appendage, wide and trian- 
gular at its origin, rapidly tapering to a rounded extremity, equalling that of the lateral angles in size and shape ; 
surface covered with a small, very unequal scattered granulation. Length of head excluding the neck-segment 
two and half lines, length of produced neck segment three and half lines, width at base of cheeks six lines. 
Position and Locality ——Not uncommon in the Wenlock limestone of Dudley; of small size in the olive- 
schists Blain y Cwm, W. of Nantyre, Glyn Ceiriog, Denbighshire. 
Genus. STAUROCEPHALUS (Barr.) 
Syn.— = Staurocephalus + Trochurus. - 
Gen. Char.—Cephalic shield granulose, front half of the g/abella spherical, posterior half abruptly con- 
tracted to a small cylindrical neck, marked on each side with two minute segmental furrows, exclusive of the 
neck-furrow, which is very broad and deep ; neck-segment large, with a short spine on its middle; cheeks trian- 
