PTERYGOTUS ANGLICUS. + eB 
except near its proximal or attached end, but it is ornamented with rough, blunt 
squamee and serrations along the lateral margins. 
The telson figured on Pl. VI is the largest known, and measures nine inches in 
length by seven inches in breadth. 
In describing the divisions of the body in Péferygotus anglicus, we have spoken of the 
head and the body, avoiding the terms “ thoracic” and “ abdominal somites” as much as 
possible. On reference to the restored figure at Plate VIII, fig. 1, it will be seen that 
there is evidence, according to the paired appendages (see andé, p. 6), of 7 somites having 
coalesced to form the cephalic division. 
Assuming that all the segments united to form the head are represented by pairs 
of appendages, we have then a true Cephalon ; the 7 succeeding free somites are thoracic, 
the abdomen being represented by 5 somites’ and a telson, or terminal joimt. But 
assuming the antennules to be wanting (see anfé, p. 37), we must conclude the head to 
represent 8 coalesced segments, that is to say, 7 cephalic and 1 thoracic, the latter 
bearing the ‘‘ operculum,” or “thoracic plate” (Pl. VII. fig. 1 op). 
In this case only the first six anterior somites will be counted as thoracic, the 
posterior six will be reckoned as abdominal, and the ‘telson’ will make up the 21 
segments. 
The likeness which Péerygotus offers to Limulus is very much strengthened by this 
latter view. As we proceed to the illustration of the other genera belonging to this 
order, we shall be still more strongly impressed with the many points of close resemblance 
which they will be found to exhibit. . 
The Merostomata seem, in fact, to present us, in these early times, with a parallel 
group of Crustacea to that embraced in the order Decapoda at the present day; the 
Macroura being represented by Plerygotus and its allies, the Brachyura by Limulus, &c., 
and the intermediate forms, like /Zemiaspis, &c., being comparable to the Axomoura. 
We could scarcely, in the whole Zoological Kingdom, point to a stronger illustration 
of the persistence of type than is to be observed in these Palaeozoic forms. 
From our present knowledge of the almost perfect remains of Pferygotus anghcus, 
and on the evidence of the numerous detached portions of this extinct genus, we are 
justified in concluding that it attained a length of six feet, and a breadth of nearly 
two feet at the widest part of its body. 
From its large eyes, its powerful natatory appendages, and from the general form of 
its body, we may also infer that it was a very active animal. Its great prehensile 
antenne and rows of serrated jaws, further indicate its predacious habits, whilst from its 
size it must have been the shark of the Devonian seas. 
“No existing Crustacean,” observes Prof. Huxley, “has so massive a body as 
Pterygotus,’ . . . . “but mass in an active animal involves large muscles, and 
See Dr. Milne-Edwards’ observations on arrested development, anté, p. 6. 
