1472 THE VOYAGE OF H.M.S. CHALLENGER. 



the first perseopod in his species is a little longer than the second, whereas both in 

 Platyscelus and Hemityphis the reverse is the case ; this would tend to show either that 

 Dana's genus is different from both those mentioned, or that no extreme weight is to be 

 given to his accuracy in niinutias. The long perseon shown in the full figure of Ditliyrus 

 /aba is more like that of a species of Platyscelus than it is to those hitherto figured of 

 Hemityphis, and, in the absence of other evidence, it seems just that Hemityphis, Clans, 

 which can be perfectly well recognised, should hold its place, and that the name, 

 Dithyrus, Dana, should stand aside until some species has been found to correspond 

 with Dana's definition. 



Hemityphis tenuimanus, Claus (PL CLXXXIIL). 



1879. Hemityphis tenuimanus, Claus, Die Gattungen und Arten der Platysoeliden, p. 12. 



1887. Dithyrus tenuimanus, Bovallius, Systematical List of Amph. Hyper., Bihaug. till K. 



Sveusk. Veteusk.-Akad. Handl., Bd. 11, No. 16, p, 46. 

 1887. Hemityphis tenuimanus, Claus, Die Platysoeliden, p. 38, Taf. iv. figs. 1-13. 



The Head broad, sloping a little downwards and forwards, the rostral angle not pro- 

 jecting but folded underneath ; the peraeon with evenly convex sides as viewed from 

 above, all the seven segments very short, so that all of them together at the centre of the 

 back do not equal the length of the head or one-third the length of the pleon ; on the 

 other hand the greatest width of the animal is at the centre of the peraeon ; the first 

 three segments of the pleon are long, the first about as broad as the head, the two 

 following successively narrower ; the sides are carinate, the hind borders below the carina 

 being emarginate ; the fourth segment is much shorter but not much narrower than the 

 third ; the fifth and sixth segments and the telson are coalesced, forming a triangular 

 piece, of which the sides are a little convex near the base, slightly interrupted at the 

 insertion of the third uropods, but otherwise converging in a nearly straight course to 

 the narrowly rounded apex. 



Eyes large, leaving the front of the head and a small triangular space behind free, 

 the lower division of the eye much smaller than the upper, not projecting so far forward, 

 and with smaller ocelli. 



Upper Antennae placed very close together on either side of the rostral point, and 

 projecting very slightly beyond the head ; first joint of the peduncle cylindrical, rather 

 longer than broad, second and third joints obscure or obsolete ; first joint of the flagelluni 

 much longer than the peduncle, bent abruptly at right angles to it, fringed on the 

 inner side with a great number of rows of filaments, set so closely as to make a thick 

 brush which streams out beyond the succeeding joints ; the distal end of the joint is 

 itsell a little produced on the inner side, with a rounded apex ; the next joint is very 

 small, about twice as long as broad, carrying several filaments, and reaching a little 



