148 
CLASS CRUSTACEA. 
ordinary teetli. The third articulation of the external jaw- 
feet is obtuse and emarginated. The eyes are much thicker 
than their pedicles, and globular. We know as yet but a 
single species which has been found on the coast of Devon- 
shire, and which M. Dorbigny, the correspondent of the 
Museum of Natural History, has also observed on our mari- 
time coasts of the western departments. ( Polybius Henslowii , 
Leach.) 
In all the following swimmers, the two posterior feet alone 
are fin-like. We may at first detach from them those whose 
testa is almost ovoid, narrowed and truncated transversely in 
front, whose tail presents distinctly in the males (the only in- 
dividuals known) seven segments. Such are, 
Orithyia, Fab., 
Only species known, O. Mamillaris , Fab. Cancer bimacu - 
latus, Herbst. 
The testa of the last swimmers is notably wider in front 
than behind, in the form of a segment of a circle, narrowed 
towards the end, and truncated, so as either to represent a 
trapezium, or approach very nearly the shape of a heart. 
Its greatest transverse diameter generally exceeds its oppo- 
site diameter. The tail of the males presents but five seg- 
ments instead of seven, the number of those in the female, 
and which is generally proper to the tail of the decapods. 
The third and the two following are confounded together, or 
form but one, nevertheless we discover the traces of them, at 
least on the sides. 
We shall separate at first those whose eyes are supported 
on slender and very long pedicles, proceeding from the middle 
of the anterior edge of the testa, prolonged as far as its lateral 
angles, and lodging in a groove formed under the edge. 
