DESCRIPTION OF THE SPECIES OF PTERYGOTUS 235. 
form), and thence tapering to the abruptly curved tip, which bends up 
at a right angle, and is frequently half an inch long and pointed. The 
opposed free claw is of the same shape, but more equal in breadth, 
generally longer, fig. 2, than the other, but sometimes the two are 
nearly equal (fig. 1). Occasionally the moveable joint is largest, fig. 6, 
and overhangs the other considerably. 
It is difficult to say which was anterior, but from the curvature 
probably the free joint was forward, as in our figure. Each half of 
the forceps similarly armed with about four primary and ten or 
eleven secondary teeth, three or four between each pair of primaries. 
These are set on at right angles, or rather pointing a little forward 
on the fixed finger, but on the moveable claw decidedly backwards. 
They appear to have been much compressed, and were so long that 
when the chela was closed they shut side by side like the blades of 
a pair of shears; and they are placed opposite to one another as if 
for the purpose of cutting as well as seizing. The middle pairs are 
longest, sometimes measuring half an inch. The pair next outwards 
from these are nearest in size, and the outermost and innermost pair 
(when the latter are present) are smallest. 
The shape of the large teeth and of many of the smaller is ovato- 
lanceolate, constructed just above the immediate base, and then 
expanded into a lancet form, and longitudinally striated, the stria 
radiating a little from the base on the forward edge. Some of the 
smaller teeth are simply conical, and the striation of all is about 
equally coarse. 
Endognaths, Plate VII. [Plate 18] figs. 4 to 7—There are five 
or six specimens in the Scotch collections more perfect than that 
figured by Agassiz (middle left-hand figure), and of larger size, fully 
four inches and a half long. The palpus, ¢ @ e, was probably five or 
six inches in length, and of considerable thickness. Some fragments 
even indicate a still larger size for the jaw. 
The mandible is of an oblong form, the front and back margins. 
nearly parallel. The serrate termination of the lamina scarcely at 
all expanded into a lobe, and the posterior or basal portion (fp). 
which occupies nearly half the entire length is produced obliquely 
backwards at a wide angle. This portion is straight in front and 
only slightly sinuous along the hinder edge, which shows traces here 
and there of striae perpendicular to the edge, probably due to the 
insertion of muscular fibres. 
The serrate edge is nearly straight and very oblique, forming an 
angle of about 120° with the front margin. There are about twelve 
strong teeth, of which the upper six or seven are free, lanceolate, 
