236 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
curved, and dilated below, with a constriction as if articulated, and 
the remainder are connected so as to form ridges upon a thin plate 
Minute intermediate ridges occur between these. The posterior 
angle of the serrate edge is produced a little into a small lobe 4, 
covered with deep punctures as if for the insertion of stiff hairs or 
sete. The upper edge is not at all expanded or overhanging as in 
P. acuminatus, the teeth starting at once from the upper angle in a 
line continuous with the front margin (this is not the case with fig. 7, 
in which there is an overhanging lobe). 
The general surface of the mandible is covered with obscure plice, 
which become distinct and large along the front margin, which is 
thickened ; the rest of the lamina is rather flat, the base is thin and 
almost membranous at the edge. 
The palpus is long and stout, directed straight outwards, and 
consisting of at least five, and probably more joints, of which the 
basal one (c) is more than twice as wide as long. The next (@) 
unceolate and thickened at the distal end, rather longer than wide. 
The third takes an elongate form, but is still broad, and its end 
thickened and somewhat bilobed (e). The next (/) is still longer 
in proportion, swelled, and a little crenulate or spiny at the tip 
(compare with Plate IX. [Plate 20] fig. 7). We have no more 
joints, but in Agassiz’s figure the succeeding joint, the fifth, is clearly 
shown. 
The surfaces of all these joints are covered with transverse plice. 
Maxilla? fig. 7—It is probable that fig. 7 indicates a second pair 
of endognaths, since the proportions of the plate are so different, 
fig. 7 being considerably longer before the insertion of the palpus 
than fig. 4, and having an overhanging rounded lobe in front above 
the insertion of the teeth. Some specimens agreeing with this in 
proportion have the basal lobe of the palpi broader. 
Swimming Feet (Ectognaths), Plate VI. [Plate 17] figs. 1 to 3, 
Plate VII. [Plate 18] figs. 1 to 3—The large basal joints of these 
organs are among the most characteristic parts of Pterygotus, and were 
at first supposed to be the mandibles or maxilla, as they are most 
frequently found detached from the other joints of the limb. Agassiz 
figured a portion as a part of the tail flap, and we reproduce his 
original specimen, Plate VII. [Plate 18] fig. 3. It will be best to 
describe this portion first. It is the— 
Basal Joint (Coxognathite), Plate VII. [Plate 18] figs. 1 to 3.— 
These are six inches and a half and even seven inches long! and not 
less than three inches broad, gently curved (flask-shaped) convex, 
with the outer or forward edge thickened, and concave on the inner 
