680 THE VOYAGE OF H.M.S. CHALLENGER. 



The telson is dorsally flat, with the sides depressed and the longitudinal line between 

 the two strengthened by a ridge and armed with four long sharp spines, the posterior 

 being situated at the terminal angles. These spines are evidently under the will 

 and control of the animal, and are capable of being erected so as to be perpendicular 

 to their base, and of being used as offensive weapons. This appears still more 

 evident from the fact that the animal has the power of becoming dorsally flexed 

 considerably beyond a horizontal line, the extent of which is shown in the shortness 

 of the dorsal length of the first two somites, which are transversely bisected by a narrow 

 groove. 



Observations. — This species presents several points of extreme interest, which I do 

 not think can be considered as generic. One is the extreme length of the two posterior 

 pleurobranchise; in the largest specimen they are so long that their apical extremities 

 are reflexed and folded back against the upper surface of the branchial chamber. Another 

 feature of interest is the deep cleft that exists, more particularly in the fifth somite, 

 between it and the coxal plate which belongs to it. Again in several congeneric forms 

 in this small group, the dorsal crest is armed with teeth, in others with spines, and 

 in some with both teeth and spines. In this genus the rostrum is armed entirely, 

 both above and below, with sharp teeth that in this species are anteriorly directed 

 almost parallel with the general line of the animal, but it is worthy of notice 

 that several of the posterior teeth show a depression or groove at the anterior basal 

 portion, apparently indicating a tendency for the conversion of the rigid teeth into 

 movable spines. 



Dorodotes levicarina, n. sp. (PI. CXII. fig. 5). 



Carapace smooth, lateral carinse subdued ; median dorsal line slightly carinated and 

 armed with eleven teeth, the posterior standing on the pyloric region and the anterior 

 near the apex of the rostrum, which is half the length of the carapace, and on the lower 

 side with six small teeth. 



Pleon slightly compressed, dorsally carinated, the carina on the third, fourth and fifth 

 somites terminating posteriorly in a small tooth. 



Telson tapering, not longer than the outer rami of the rhipidura. 



First pair of antennae scarcely longer than the rostrum. 



Second about half the length of the animal. • 



Outer rami of the rhipidura broad and furnished with a diseresis, the outer angle of 

 which is near the distal extremity. 



