EURYPTERUS SCOULERI. 137 



The remains referred to give evidence of two individuals differing considerably in size ; 

 the head-shield of the larger specimen (PL XXVII) measuring 8 inches in breadth and 

 6 inches in length along the convex dorsal surface of the shield, whilst the smaller, 

 (PL XXV) measures 7 inches in breadth and 5^ inches in length. 



Fig. 42. — (a) Diagram of articular surface of posterior border of one of the body-rings of Eurypterus Scouleri. 



(b) Diagram of longitudinal section of body -rings of same, showing the mode of articulation of the segments ; 

 t, t, tergal pieces ; a, a, infolded articular borders. 



The detached series of posterior segments figured on PL XXVI may have belonged 

 to an individual equal in size to that represented by the lesser head-shield. The posterior 

 segments show a considerable increase in length, as compared with the two most anterior 

 (thoracic) rings, but they have also diminished considerably in breadth. 



These two anterior body-rings (attached to the head, see PL XXVII) are ornamented 

 with a single row of narrow, acute, well-defined, spine-like squamse, very like those on 

 the posterior border of the head-shield. They are each 6-g- inches in breadth along the 

 dorsal surface and f ths of an inch in length. 



The posterior free margin of the series of abdominal somites (PL XXVI) is ornamented 

 on its dorsal border with a series of blunt, rounded, equidistant spines, and the surface 

 itself is covered with squamae (PL XXVI, figs. 1 and 3), whilst the ventral border of the 

 larger segments is roundly dentated (figs. 2 and 4), and that of the penultimate segment 

 is more acutely so (fig. 5). The ventral surface is not covered with squamae, but is 

 finely punctate, reminding one of the structure of the carapace in many Brachyurous 

 Crustaceans. 



The circumference of the xnth segment is 10| inches, and the breadth of its dorsal 

 surface 5^ inches. That of the xviith is 8-| inches, and the breadth of its dorsal surface 

 4 inches. Girth of the penultimate segment 5 inches, breadth 2\ inches. The length of 

 the 8 posterior segments, measured down the dorsal line, is 6^ inches. 



Guided by the two thoracic segments (PL XXVII), and by the series of united 

 abdominal segments seen in Mr. Powrie's specimen (PL XXVI), I have prepared a 

 drawing of the entire body of E. Scouleri to the scale of the larger head-shield figured on 

 our PL XXVII, from which I estimate the entire body to have been 22 inches in length 

 divided as follows : 



20 



