436 GEOLOGICAL SURVEY OF THE TERRITORIES. 
the course taken by the blood in passing through the gill and accessory 
gill or flabellum, and that it must also be partly aerated by the jointed © 
endopodite; the entire appendage, therefore, as in those of the Branchi- 
podida, is concerned in respiration. It will thus be seen that the limb 
is lamellated, but differs essentially from the Phyllopodous limb in 
that the endopodite is simple, the axis multiarticulate, but sending off 
no endopodal lobes from the axites, such as form the characteristic feature 
of the Phyllopodous foot. From overlooking this important and radical 
difference from the Phyllopodous foot the earlier observers were led to 
place Nebalia among the Phyllopods. 
In comparing the thin, lamellar thoracic foot of Nebalia with the thor- 
acie foot of any Decapod from Cuma to Mysis, and up through the Ma- 
crura to the crabs, it will be found impossible to homologize the parts 
closely, though a general homology is indicated, the endopodite of the 
Nebalia and the gills corresponding in a general sense to those of the 
Decapods, and itis this lack of close homology more than any other which 
forbids us from regarding the Nebalide as entitled to take rank under the 
order of Decapoda, or with any of the Malacostraca. But when we compare 
the thoracic legs of the adult Nebalia with the maxillipedes of the zoéa of 
the Decapods, then we can detect a slight and interesting resemblance, 
but the resemblance and homology is not so close as between the thor- 
acie legs of the Phyllopods and the maxille of the early zoéa. 
On comparing the broad lamellate thoracic feet of the adult Nebalia 
with the rudimentary thoracic feet of the later stages of the zoéa the re- 
semblance is but slight. Just before the zoéa passes into the adult con- 
dition the five pairs of thoracic feet of the adult bend out as two-lobed 
processes; but the resemblance to the leaf-like foot of Nebalia is too re- 
mote to be of any taxonomic value; and this remote resemblance shows 
that Nebalia does not belong to the Decapod type. 
The six pairs of abdominal feet (Plate XX XVII, figs. 4, 5).—Turning 
to the abdominal feet, we find that they are simple, without gills, and 
entirely different from the leaf-like thoracic appendages, and we have 
in this differentiation of true abdominal from the thoracic feet a Mal- 
acostracan character, one quite unlike the differentiation or blending 
of the two regions in the Phyllopods. 
The abdomen is nine-jointed, the segments cylindrical and edged with 
obtuse spines (Pl. XXXVI, fig. 8.) much as in Copepoda. 
-The segment succeeding the 8th thoracic is much larger and extends 
farther down sternally than the 8th thoracic, and bears a large, stout 
pair of feet, to which the three following pairs are closely related in form. 
For example, the 2d pair (Pl. XX XVII, fig. 4) consists of alarge, thick, 
long stem (protopodite) which sends off three appendages, an outer (ex- 
opodal) stout, blunt appendage, (ex); edged with stout sete externally 
and more densely on the inner edge with ciliated, delicate sete the mid- 
dle two-jointed appendage (endopodite, en) is longer and slenderer than 
the outer, and edged externally with finer sete; a third minute bract-like 
appendage, Claus says, acts as a retinaculum (Irig. 4, ret.) to connect 
the two legs of the same pair while the creature is in the act of swim- 
ming. Intheir general form the abdominal legs appear to resemble the 
simple biramous legs of the Copepoda, but still more closely those of the 
Amphipoda, in which, as Claus observes, there is a similar retinaculum. 
(See also Milne-Edwards’s Crustaces, Pl. 30, fig. 3?.) 
The 5th and 6th segments of the abdomen bear much smaller, more 
rudimentary legs. The first pair (Pl. XX XVII, fig. 5) are seen to be 
two-jointed, the 2d joint long and slender, bearing near the end stout 
raptorial setz, and on the inner edge slender setz. The 6th pair are 
