866 The Crustacean Nebalia and its Fossil Allies, [November, 



or flabellum of the Phyllopod foot, this flabellum being as long 

 as the entire endopodite, but not quite so broad as the gill, the 

 distal portion of the flabellum is more pointed than the proximal, 

 and, as will be seen by referring to the figure, is more actively 

 engaged in the process of respiration. The figure shows by the dot- 

 ted lines of parenchymatous matter 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 en- 

 tire appendage, therefore, as in those of the Branchipodidae, 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 multiarticular^, but send- 

 ing off no endopodal lobes from the axites, such as form the 

 characteristic feature of the Phyllopodous foot. From overlook- 

 ing 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 thoracic foot of any Decapod, from Cuma to Mysis, and up 

 through the Macrura to the crabs, it will be found impossible to 

 homologize the parts closely, though a general homology is indi- 

 cated, the endopodite of the Nebalia and the gills corresponding 

 in a general sense to those of the Decapods, and it is this lack of 

 a homology more than any other which forbids us from regard- 

 ing the Nebalidae as entitled to take rank under the order of De- 

 capoda, or with any of the Malacostraca. But when we compare 

 the thoracic legs of the adult Nebalia with the maxillipedes of 

 the zoea of the Decapods, then we can detect a slight and inter- 

 esting resemblance, but the resemblance and homology is not so- 

 close as between the thoracic legs of the Phyllopods and the 

 maxillae of the early zoea. 



On comparing the broad lamellate thoracic feet of the adult 

 Nebalia with the rudimentary thoracic feet of the later stages of 

 the zoea, the resemblance is but slight. Just before the zoea 

 passes into the adult condition 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 remote to be of any taxon- 

 omic value ; and this remote resemblance shows that Nebalia 

 does not belong to the Decapod type. 



The six pairs of abdominal feet (Plate xiv, Figs. 4, 5). — Turning 



