IV. THE OXYCEPHALIDEA^ GE1SERA A1SD SPECIES, 



As I have already said I think it convenient to divide the Oxyce- 

 phalids into two families, instituting a new family Xiphocephalidse for 

 the genus Xiphocephalus. I separate this genus from the other Oxy- 

 cephalids, because it is distinguished from the other genera by charac- 

 teristics which in my opinion have a more than generic value. So for 

 instance Xiphocephalus has the seventh pair of pereeopoda rudimen- 

 tary, arid consisting of only the femur, while the other genera have the 

 same pair complete 1 ); Xiphocephalus normally has the telson free from, 

 and articulating with, the last ural segment, while all the other genera 

 have the telson fused with the last ural segment; and lastly the female 

 of Xiphocephalus wants ovitectrices, and carries the eggs and young 

 fixed under the peraeonal segments in two regular rows, while the other 

 genera have well developed ovitectrices. On the other hand the two 

 families are connected by some common characteristics, as for instance 

 the reduction of the mouth-organs, the maxillae being rudimentary in 

 both families, and the rostral elongation of the forepart of the head, 

 and the more pronounced tendency to form an elongated body than is 

 seen in any other family of the tribe. This tendency to elongation is 

 besides expressed in the form of the femora of the fifth and sixth pairs 

 of perseopoda in Xiphocephalidae, but not met with in these parts in 

 Oxycephalidae, not even in the genera Leptocotis and Calamo- 

 rhynchus, which show much elongated uropods. 



DANA was the first (17, p. 1009, see above, p. 5) who took the 

 Oxycephalids as a whole placing them as a subfamily, Oxycephalince, 

 of the family Typhidce, at the side of the subfamilies Typliinoe and Pro- 

 noince; he then gave the following diagnosis of the Oxycephalince: 



Abdomen in ventrem se non flectens. Caput oblongum, antennis 

 Imis superficiem capitis inferiorem insitis)). 



1) Except Tullbergella which has the femur and three following joints. 



