EEPOET ON THE CRUSTACEA MACRURA. 433 



" Pleon having the fourth, fifth, and sixth somites armed with a small sharp tooth on 

 the posterior margin of each. The first to the fifth somites also furnished with a sharp 

 tooth on each side, especially distinguishable on the fourth and fifth. 



" Sixth somite of the pleon exceeding the fifth part of the length of the animal, or 

 equalling that of the third, fourth, and fifth somites combined, and three times as long 

 as the telson, linear, and three times as long as broad. 



" Pleopoda very slender. 



" Ehipidura having no tooth on the outer margin of the outer branch. 



" Habitat. — Greenland," (Kroyer). 



I can recognise no form corresponding exactly with this species, but the next, 

 Sergestes utrinquedens, differs from it in having a longer and more slender rostrum and 

 a longer telson, and in having no teeth on the dorsal surface of the pleon. 



Sergestes longirostris (p. 415, PL LXXV. fig. 3), differs from it in having a tooth on 

 the outer plate of the rhipidura. 



Sergestes utrinquedens, n. sp. 



Carapace more than one-third the length of the animal not including the rostrum, 

 which is straight, slender, and nearly as long as the ophthalmopoda. The frontal 

 margin is rounded and smooth, but just beyond the fronto-lateral angle is a small 

 anteriorly directed tooth. The rest of the carapace is free from ornamentation. 



The pleon has the four anterior somites subequal, and all ventrally smooth and 

 dorsally unarmed ; the fifth is slightly longer than the preceding, and all these five 

 somites have the lateral or coxal margins pointed and tipped with a strong sharp tooth, 

 the first which is the largest has the smallest tooth, and the fourth which is the smallest 

 has the largest tooth. The first somite is, moreover, furnished on each side with a 

 small projecting process that corresponds to the pleocleis in other genera. The sixth 

 somite is as long as the two preceding and is dorsally armed on the posterior margin 

 with a small and slender tooth, and the postero-lateral angles are produced to a very 

 minute point. 



The telson is about as long as the last somite, and is produced into two sharp 

 terminal points, flanked on each side with two small teeth or spines. 



The ophthalmopoda are about half the length of the carapace ; the ophthalmi broader 

 than the stalk, which gradually tapers to the base. 



The first pair of antennae has the three joints of the peduncle subequal ; the first joint 

 is rather the longer, it is enlarged at the base to receive the otocyst, and is armed on the 

 outer margin with a sharp tooth ; the two succeeding joints are cylindrical and support 

 flagella that are broken off. 



(ZOOL. CHALL. EXP. — PART LII. — 1887.) Fff 55 



