Crusracea.| LOWER PALAOZOIC ARTICULATA. 175 
surround it are toothed and shaped so as to serve for mastication. The head and thorax are confounded 
under one semicircular shield-like carapace. 
There seem to be only two families: Ist, Limulide, having the abdominal segments anchylosed into 
a shield (Limulus, §c.) 2nd, Eurypteride, with the abdominal segments distinct, simple (Hurypterus, 
Pterygotus, Bellinurus, &c.) 
Genus. EURYPTERUS (/Harlan.) 
Gen. Char.—Body crustaceous, elongate, ovate, very convex, attenuated posteriorly; cephalo-thorax 
covered by a small, semiorbicular or rotundato-quadrate shield, truncate behind, margin obscurely depressed, 
often with a faint V-shaped, re-entering angle in front; two large reniform eyes, one on each side of the 
middle of the cephalic shield; at least three pairs of large, unequal, crustacean, didactyle, thoracic legs ; 
abdomen semicylindrical, of thirteen distinct, transversely arched segments, gradually narrowing towards the 
terminal one, which forms a short spine, serrated on the sides as in Limulus. 
I have little doubt, from the figure, and description of Conrad and Rémer (see the paper on the 
American species in Dunker and Von Meyer, “ Beitrdge zur Naturgeschicte der Vorwelt,” &c.), that the 
present genus is closely allied to Limulus; we might therefore expect that the thorax would bear crustacean 
prehensile feet, but each joint of the abdomen a pair of membraneous gill-feet. 
EURYPTERUS CEPHALASPIS (Salt. Sp.*) Pl. 1. E. fig. 21. 
Ref. and Syn.—Homalonotus cephalaspis Salt., in Appendix to Ray ed. of Burmeister, p. 125. 
Sp. Ch.—Cephalic shield semielliptical, length one inch, width one inch three lines, strongly and evenly 
convex, the anterior and lateral arched margins with a narrow, flattened, horizontal rim, all in one plane, 
with the edge deflected; posterior margin simple, truncate, elevated by the general convexity; cyes hiant, 
obscurely reniform, about three lines long, four lines apart, and their own length within the front margin ; 
a very obscure indication of a mesial ridge branching at an acute angle from between the eyes towards 
the front; surface obscure. 
This is about double the linear measurement of the head of the Z. tetragonophthalmus of Fisher 
(Bull. de la Soc. Imper. des Natur. de Moscou. Vol. for 1839). 
Position and Locality Rare in the hard green micaceous quartzite of Kirkby Moor, Kendal, West- 
moreland. 
Explanation of Figure—PI. 1. E. fig. 21. Head, natural size. 
PTERYGOTUS LEPTO-DACTYLUS (M‘Coy). Pl. 1. E. fig. 7. 
Ref—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IV. 
Sp. Ch.—Scale-like sculpturing of the surface very irregular, but of two principal very unequal sizes, 
the larger about six times the size of the smaller and more numerous size, averaging rather less than one 
line in diameter ; large pincers having the hand about five lines wide, the penultimate or immoveable finger 
compressed, about two inches ten lines long, and two lines wide at base, gradually tapering to less than 
a line towards its obtuse point, nearly straight, with a scarcely perceptible inward curvature; sides divided 
into ridges by three or four longitudinal furrows, thicker towards the back, inner edges of both fingers 
destitute of teeth or tubercles; moveable finger similar to the immoveable one, but rather smaller, 
* Mr Salter, on becoming aware of my referring his species to Zurypterus, instead of to the trilobites, now adopts 
the same view. 
