DESCRIPTION OF THE SPECIES OF PTERYGOTUS 225 
Lastly, we have a very perfect head of the species, here given, 
fig. 8, which shows the palps ¢w s7¢z, and there is so strong a 
divergence between the front filament a, and the lower one 4, as 
to render it probable they are not mere branches of the same palp. 
Fic, 8. 
LP. acuninatus ; rather more than one-third natural size. Lesmahago. Mus. Prac. Geol. 
Specimen showing both first and second pairs of palpi, u, 4, and the swimming foot c. 
bis far more imperfect than a. ¢, is the swimming foot (ectognath) 
im situ. 
Swimming Feet, figs. 5 to 9—The great basal joints of these 
organs are squarer in outline and their serrate edges placed more 
vertically (ze. more parallel to the general direction of the plate) than 
in P. bilobus or P. anglicus, Plates I., VII. [Plates 12, 18], in 
order apparently to accommodate their shape to the elongate form 
of the head. The terminal joints, too, of the limb are less expanded 
and more linear than in the above-mentioned species. 
The size of the largest fragments would give about four inches 
and a half for the length by two inches and a half broad. The great 
subquadrate basal joint occupies full two-thirds of the length ; it 
is straight along the inner margin, rather square at the outer and 
upper angle, rounded on the outer side, and has the notch for the 
attachment of the remaining joints deep. On the lower third, behind 
which the breadth lessens, the basal margin is convex. The entire 
joint is thickened, and most so from the notch obliquely upwards ; 
VOL, IL Q 
