224 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
occur scattered over the surface, and particularly on the outer 
edges and down the middle. They are also in parts ornamented 
with minute plice parallel to their length. It is not quite certain 
if ¢ and @ are single joints, or two styles parallel to one another 
and pressed closely together, ¢ is probably a pair of joints, as 
besides the crested spiny edge, it is furnished with a pair of thick 
curved spines (like those of the succeeding joints) on each half. 
ef gin the longer filament are of less diameter, successively shorter, 
but still thickened at their ends, and furnished with thick curved 
spines three or four in number; the terminal joint %, 7, in both 
filaments is a strong simple curved spine, without a striated surface 
or any serrations to the border. These terminal joints are not well 
seen in the large specimen figured in Plate XIV. [Plate 25], but 
the proximal joints are more perfect. 
The position given to the palpus in this plate XIII. [Plate 24] 
with the spiny crests directed forwards, is in conformity with the 
position of the much larger spines in P. punctatus, fig. 9. 
It is difficult to prove the existence of two separate manillary 
pieces from any of these specimens (Plate XIII. [Plate 24] fig. 2, 
affording the best evidence on this point). But it seems pretty clear 
Fic. 7. 
P. acuminatus, an endognath with a simple palpus; two-thirds of the natural size. 
Museum of Practical Geology. 
that there were two palpi on each side, one simple, the other branched 
from near its base:—the number of joints before branching cannot 
be stated with certainty. If only two filaments be admitted on each 
side, the alternatives will be—a single mandible with a branched 
palpus,—or two mandibles each with a simple palpus. We have 
fortunately met lately with a specimen (fig. 7), tolerably perfect, 
and showing the basal serrate joint, with six simple joints follow- 
ing; the terminal uncinus is lost. There must, therefore, be two 
jaws, one of which has a simple palp: the other most probably a 
branched one. 
