436 GEOLOGICAL SUEVEY OF THE TEREITORIES. 



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 Branclii- 

 ])odidcE, is concerned in resj^iration. 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 

 noendopodal 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- 

 acic foot of any Decapod from Guma to Mysis, and up through the Ma- 

 crura to the crabs, it will be found imi^ossible to homologize the parts 

 closely, though a general homology is indicated, the endopodite of the 

 Kebalia and the gills corresponding in a general sense to those of the 

 Decapods, and it is this lack of close homology more than any other which 

 forbids us from regarding the Nehalidce as entitled to take rank under the 

 order of Deca^poda, or with any of the Malacostraca. But when we compare 

 the thoracic legs of the adult ISTebalia with the maxillipedes of the zoea 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- 

 acic legs of the Phyllopods and the maxillae of the early zoea. 



On comparing the broad lamellate thoracic feet of the adult Kebalia 

 with the rudimentary thoracic feet of the later stages of the zoea the re- 

 semblance is but slight. Just before the zoea passes into the adult con- 

 dition the five pairs of thoracic feet of the adult bend out as two-lobed 

 l)rocesses ; but the resemblance to the leaf-like foot of Il^ebalia is too re- 

 mote to be of any taxonomic value ; and this remote resemblance shows 

 that Kebalia does not belong to the Decapod type. 



The six pairs of abdominal feet (Plate XXXVII, 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 (PI. 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. 

 Por example, the 2d pair (PI. XXXVII, fig. 4) consists of a large, thick, 

 long stem (protopodite) which sends off" three appendages, an outer (ex- 

 opodal) stout, blunt appendage, {ex) ; edged with stout setae externally 

 and more densely on the inner edge with ciliated, delicate setae the mid- 

 dle two-jointed appendage (endopodite, en) is longer and slenderer than 

 the outer, and edged externally with finer setae ; a third minute bract-like 

 appendage, Claus says, acts as a retinaculum (Fig. 4, ret.) to connect 

 the two legs of the same pair while the creature is in the act of swim- 

 ming. In their general form the abdominal legs appear to resemble the 

 simple biramous legs of the Copepoda^ but still more closely those of the 

 AmpMpoda, in wiiich, as Glaus observes, there is a similar retinaculum. 

 (See also Milne-Edwards's Crustaces, PI. 30, fig. 3^) 



The 5th and 6th segments of the abdomen bear much smaller, more 

 rudimentary legs. The first pair (PI. XXXVII, fig. 5) are seen to be 

 two-jointed, the 2d joint long and slender, bearing near the end stout 

 raptorial setae, and on the inner edge slender setae. The 6th pair are 



