XII 
BRITISH FOSSILS 
PART IT—DESCRIPTION OF THE SPECIES OF 
PTERYGOTUS 
By J. W. SALTER, F.G.S., A.L.S. 
Memoirs of the Geological Survey of the United Kingdom, Monograph T., 
1859, PP. 37—105. 
PTERYGOTUS. Gen. Ag. 
THE generic characters have already been detailed in the intro- 
ductory portion of this memoir. It is only necessary here to give 
them in brief, and point out the two very distinct sections or sub- 
genera into which the group may be divided. These sections are 
indicated by the form of the head, the position and outline of the 
eyes, the shape of the labrum and palpi, and probably, too, by that of 
the terminal abdominal segments. 
Genus PTERYGOTUS, Acassiz, 1844. (Class Crustacea, Order Eurypterida). Carapace 
small, semi-oval or subquadrate, with lateral eyes, followed by 12 body segments unfurnished 
with appendages, the twelfth being a large telson, pointed or acuminate, or blunt and 
bilobed ; epistoma large, deeply trilobed ; antenne of few (4) joints, strongly chelate ; 
mandibles (and maxillze ?) with palpi of 6 or more joints; metastoma ovate, large, notched 
anteriorly ; a large pair of ectognaths, their terminal joints expanded for swimming, and the 
great foliaceous basal joint furnished with an inner serrate lobe or process. 
Section 1. Carapace semi-oval, produced in front beyond the elongated lateral eyes ; 
labrum with its middle lobe ovate ; palpi linear, simple ; bases of swimming feet foli- 
aceous and overlapping each other ; the succeeding joints attached posteriorly. [Terminal 
joint or telson truncate or bilobed ; the penultimate not expanded.] 3 species. 7. bzlobus, &c. 
Section 2, Pverygotus proper. Carapace quadrate or subquadrate, seldom semi-oval or 
produced in front; eyes large, round, placed far forwards ; labrum transverse, its middle 
lobe sagittate at base ; palpi with tumid joints, fringed, or branched ; bases of swimming 
feet not overlapping each other; the succeeding joints attached more forward than in the 
last section, [Telson ovate, apiculate, or greatly produced, the penultimate joint expanded. ] 
12 species. P. anglicus, P. gigas, &c. 
It will be seen that these sub-genera contrast in nearly all points. 
The production, however, of the front margin into a semicircular 
form in one of the true Prerygot?, P. gigas, and the possibly emarg- 
inate apex to the long ovate telson of that species, show that these 
characters are not without variation. Yet even in this case the 
