228 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
The sculpture is rather obscure, strong on the anterior half of 
each segment, and faint over the rest ; the borders are smooth. 
Swimming Feet—These are the only appendages found with the 
present species; they resemble those of Pzerygotus bzlobus, and, when 
laid back, reach the end of the fifth segment. The third joint is very 
obscure ; the fourth trigonal with the longer side outwards, and but 
little convex ; the fifth irregular, its produced outer edge overhanging 
the oblong penultimate joint. 
This latter (¢) is about twice and a half as long as wide rather 
broadest at the bilobed end, the notch deep; lobes rather acute, the 
inner much exceeding the outer in size. Terminal palette ovate, its. 
length (measuring from the notch) equal to the penultimate joint 
without the lobes. Margins minutely crenate. 
Locality —Lesmahago ; only one specimen known, (Museum of 
Practical Geology.) 
Pirates III. ro VII. [PLATres 14, 18]. 
PTERYGOTUS ANGLICUS. 
Spec. Cuar. P. gigas, 6-8 ?—pedalis, capite transverso, anticd angus- 
tort truncato, segmentis corporis transversis, penultimo percarinato (subtus 
carind brevi subcentral’), vix expanso, caud& ovata breviapiculata, cariné 
mediand paullo elevata. 
Synonyms. #P. anglicus, Acassiz (1844), Poissons Foss. Vieux Gres 
Rouge, pl. 1; M‘Coy in Lyett (1855), Elem. Manual, 5th ed. pp. 419, 420 
(restored). SALTER in Murcuison’s Siluria, new edition (1859), foss. 21, 
fig 1, restored; Trans. Brit. Assoc. 1856, Rep. Sections, p. 75. Paleocarcinus 
alatus (AGASSIZ olim) fade PaGE, in Trans. Brit. Assoc., 1855, vol. xxiv. Rep. 
Sections, p. go. 
The liberality of Lord Kinnaird and of the officers of the Watt 
Institution, Dundee, has placed at our disposal a magnificent series 
of this well-known species, including most of the fragments from 
which Agassiz drew up his original description. We have also 
to thank Colonel James, Director of the Ordnance Survey, and 
Mr. David Page, of Edinburgh, for their kind co-operation. 
Until the carapace, Plate III. [Plate 14] fig. 1, was obtained, 
no very complete notion could be formed of the probable size of the 
fossil. It was a less elongated species than P. acuminatus, but 
taking the proportions of the head and the widest body rings as 
a guide, and comparing these with such species as P. dzlobus, the 
