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



Willenioes Suhm as being the young of Sergestes tenuis, but what that species is I am 

 not prepared to determine, as there is no adult in the collection thus named. 



With it was taken the Acanthosoma form represented on PI. LXIV. fig. 2 (Acantho- 

 soma tynitelsonis), in which figure a large median lobe ought to be added to the ventral 

 surface of the five anterior somites of the pleon, of which the three anterior are armed 

 with a small tooth. A younger Acanthosoma that corresponds in certain details with 

 Acanthosoma macrotelsonis (PI. LXVI. fig. l) suggests that they belong to separate 

 species. The length of our type specimen is about 4 mm. The carapace has four 

 lateral spinous teeth, but instead of being situated as in Acanthosoma macrotelsonis 

 they are all close together and implanted nearer the fronto-lateral margin ; the two 

 anterior are small, close together, and correspond with the fronto-lateral angle of the 

 carapace ; the next is long, slender, and not remarkably spinous, and the next is somewhat 

 similar and situated in a line a little posterior to the oral appendages. Behind this the 

 rest of the carapace is smooth, as in figs. 1 and 3 on the same plate, from which it 

 differs in having a long, slender, forked, and spinous telson. It corresponds with fig. 

 3, which Dr. Suhm considers to be a younger stage, in the form of the scaphocerite as 

 well as in the outer branch of the rhipidura. 



The specimen figured as Mastigopus tenuis on PI. LXV. fig. 4, was also taken 

 associated with Mastigopus spiniventralis ; its length is about 5 mm. It was 

 labelled by Dr. Suhm, whose name I have retained, as being the young of Sergestes 

 tenuis ; it is an older form, and has assumed the Mastigopus features, but they cannot 

 belong to the same species, for in this one the rostrum is short and rudimentary, without 

 a dorsal tooth ; it is unarmed on the dorsal surface of the pleon, destitute of teeth on the 

 median lobes of the ventral surface, and the outer branch of the rhipidura is not armed 

 with a lateral tooth. These four forms were taken together, mounted and labelled by 

 Dr. Suhm as the young of one species. Except for the large diameter of the eye, the 

 specimen corresponds more closely with the description of Sergestes edwardsii than with 

 any other species known to me. 



Sergestes profundus, n. sp. 



Carapace about one-third the length of the animal, anteriorly produced to a sharply 

 pointed rostrum, and armed on the crest with one small tooth. Dorsal surface divided 

 near the middle by the cervical fossa. First four somites of the pleon subequal in length, 

 the fifth rather shorter than the preceding, the sixth as long as the fourth and fifth 

 together. 



The antennae, gnathopoda, pereiopoda are lost, and the rhipidura is broken. 



Length, 21 mm. (0-84 in.). 



