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



Outer plate of Second Maxillse broader than the inner ; the inner margins of the 

 plates not fringed with spines or setse. 



Palp of the Maxillipeds slender, the first joint longer than the second, the fourth 

 short, unguiform. 



Both pairs of Gnathopods, but especially the second, of great length and tenuity, the 

 wrist much longer than the elongate hand, the finger very small yet making the hand 

 subchelate. 



The Second Uropods intermediate in length between the first, which are longer, and 



the third. 



The Telson undivided. 



The generic name is derived from the Greek words 6.ko.v6u. a spine, and exiws, a hedge- 

 hog or sea-urchin. The genus appears to come near both to Boeck's subfamily Epinierinse 

 and his subfamily Iphimedinse, disagreeing from his definition of the latter, however, in 

 having the last joint of the maxilliped palp unguiform. From Acanthonotozoma of Boeck 

 it differs in respect of the first maxillse and the gnathopods, and in other points. With 

 Iphimedia it is to a certain extent allied by the gnathopods, which nevertheless are to 

 some extent unique. From Boeck's Acanthozone, with which I at first identified it, it is 

 separated by the spine-row of the mandibles, the inner plate of the first maxillae, the 

 outer plate of the maxillipeds, in respect of the characters assigned to these parts in the 

 definition of the subfamily Epimerinaa, while the gnathopods in the two genera are also 

 very different. 



Acanthechinus tricarinatus, Stebbing (Pis. LXIX., LXX.). 



1883. Acanthozone tricarinata, Stebbing, Ann. and Mag. Nat. Hist, ser. 5, vol. xi. p. 205, 



March 1883. 

 1885. „ „ Stebbing, Narr. Chall. Exp., vol. i. part ii. p. 621. 



Body cylindrical, except the after part of the pleon. which is a little depressed and 

 strongly flexed. 



Head very small, almost concealed, with a small rostral angle, and two small 

 adjacent lateral lobes on either side ; each segment of the peraeon armed with three large 

 pointed processes, three-sided, with sharp, serrate edges, the central connected by a 

 transverse ridge on each side with the lateral, all three rising on the hinder part of the 

 segment ; the central process on the first segment is bifurcate, the front arm pointing 

 forwards, the hinder backwards, which is the direction assumed by those on the following 

 segments ; the length of the processes increases in each segment successively. The first 

 segment of the pleon has a long central process, like that on the last segment of the 

 perseon, and on each side two tubercles, one below the other, at a little distance from 

 the hind margin ; the hind margin itself juts out a little before reaching the angle with 



