SALTEK ETTRYPTERUS. 83 



The round prominent eyes are also set in depressions, which run 

 from them in a curved line to the inner margin of the broad posterior 

 spines on each side, and thus enclose the convex, semicircular space 

 which, lying behind the region of the eyes, is covered with thick- 

 set sjrinous squamae. Another deep triangular indentation lies 

 between two thick lobes, diverging backward, which separate the 

 eyes ; and, as these lobes are much swollen, the depression is really 

 greater than any of the others. In the midst of it lies a short, tri- 

 angular, prominent mass, broken in our specimen. Above, in front 

 of this depression, is a slight boss (which would very probably be 

 the place of the minute stemmata, were they preserved) ; but there 

 are no wrinkles nor elevations of any kind in front of the eyes. 

 The whole surface is evenly convex, divided by the semicircular 

 furrows from the rugose portion behind the eyes, as above men- 

 tioned. The margin is narrow, thickened, and raised all round. 

 The ornament of the surface is minute in front, and consists of small 

 prominent tubercles, with minute granules between them ; further 

 down the sides the tubercles become triangular squamae, with others 

 interspersed ; and these squamae become larger and larger towards 

 the ears (with raised borders and generally a strong central tubercle), 

 and attain their largest size on the posterior area, where they are 

 also narrower and more pointed, as well as stronger, than elsewhere. 

 On the extreme hinder border they become linear ridges ; and in 

 this form they also occur on the free edges of the body-segments. 

 The crust is not thick; and the squamae, except in the largest, 

 appear to be more convex and prominent beneath the crust than 

 above it, so as to indent the cast. This is particularly the case with 

 the smaller squamae, which are so concave above as to be truly convex 

 below : the margin shows this conspicuously (fig. 5) ; and wherever 

 the surface has been abraded or weathered, the hollows are much 

 deepened and exaggerated. 



The body-rings have a great convexity, as above stated ; the two 

 anterior rings are very short, not more than half an inch long even 

 in this large specimen. On the under side they expand into 

 the broad sternal flaps so characteristic of this family of Crustacea. 

 One of the swimming-feet is preserved. The basal joint is either 

 very small, compared with that of Pterygotus, or is imperfect. 

 The shape of the other three is not well defined ; but they are 

 evidently thick, carinate at the edges, and have the usual triangular 

 or wedge-like shape alternately in the lower joints. 



In Dr. Hibbert's description of Eurypterus Scouleri, he says 

 (p. 281) : — " The Eurypterus Scouleri is to be distinguished from 

 other species by the prolonged eminences intervening between the 

 eyes, which, at their apex, form an angle wherein appears a central 

 tubercle; also by the small, acutely angular protuberances, like spines, 

 which are diffused over the surface of the head beneath the eyes. The 

 characters of the feet cannot be given, as no vestiges of them, except 

 very slight ones, have turned up." In truth, there is no known spe- 

 cies with which it can be confounded, nor any approaching it in size. 



Hall's beautiful specimens have enabled him to show, what was 



6 2 



