﻿PTERYGOTUS ANGLICUS. 37 



presents a finely punctated appearance, as represented in Plate I, fig. 2a, but there is no 

 appearance of any scale-like markings upon it, as upon the appendages and somites. 



The chelate Antenna. — The very fine examples of these organs drawn on Plate VII, 

 figs. 1 — 3, from specimens in the museum of Lady Kinnaird, Rossie Priory, Perthshire, 

 and the Watt Institution, Dundee, still remain unrivalled. Three joints at least may be 

 observed in this member. " The first is an elongated subcylindrical stem, flattened by 

 pressure," in fig. 2, but retaining its normal rounded form in fig. 4; "the next, short, 

 enlarged, and swollen, is produced into a long slender process, pointed and incurved at 

 its extremity, and beset with very strong and numerous unequal striated teeth. The third 

 joint is articulated with the enlarged basal joint of the second, so that its similarly in- 

 curved extremity is opposable, like a thumb, to the latter. It possesses teeth of a similar 

 structure to those in the other ramus of the chela, and opposed to them as the canine 

 teeth in the upper jaw of a mammal are opposed to those in the lower, passing, that is, 

 behind the others, or on their proximal side. 5 ' 1 



Prom a careful comparison of these organs with the less rare and often better preserved 

 remains of Pterygotus bilobus and P. perornatus, they have been placed in front of the 

 mouth (Plate VIII, figs. 1, and 2, 2, 2). We have no evidence that the coxal, or basal joints 

 of these chelate appendages were converted into gnathites ; but the corresponding simple 

 pair of organs in Slimonia and Eurypterus (and probably also in Stylonurus), are made to 

 fulfil the office of jaws. It was probably this fact, which led Prof. Agassiz* to conclude 

 that the antennary system was entirely absent in the Eurypterida, but the antennae in 

 Limulus (see Plate IX, fig. 1, 3, and la) also act as gnathites; and if we accept Prof. 

 Huxley's view, that these chelate organs in Pterygotus represent the antennas, and assume 

 the antennules to be aborted, the remaining mouth-organs will be found to correspond 

 exactly in number, with Limulus. 



The Endognaths, or Mandibles and Maxilla? — The three pairs of organs which follow 

 after the antennas are apparently almost identical in form. 



At Plate VII, figs. 5, 6, 7 and 8, represent the best detached examples of these 

 appendages that have as yet been discovered, whilst at Plate II, fig. 1, we see several 

 nearly entire endognaths, but too small to show more than the general outline. 



The basal joint is large and flat, and produced almost to a point at one extremity 

 (figs. 5jy and 6p), where it was evidently attached to the head, and truncated obliquely to 

 its long axis at the other. The truncated margin is slightly curved, and is beset with 

 strong curved and pointed teeth, which are longer at one end of the series (a), than at the 

 other (b), and are so constricted at their bases as to appear to be articulated with the basal 

 joint {a, b, figs. 5, 6 and 7). On the outer part, immediately above the pointed extremity 

 (p), is inserted the basal joint of the long palpiform appendage. The first two (?) joints of 



1 Prof. T. H. Huxley, Surv. Mon., p. 14. 



2 Hall's 'Palaeontology of New York,' 1859 (see ante, p. 18, \ 47). 



3 This description is taken in part from Prof. Huxley's Survey Mon., p. 15 (6). 



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