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



pair of gnathopoda. The second and third pairs of pereiopoda are long, slender and 

 chelate. The fourth and fifth pairs are in a rudimentary or bud-like condition. 



The pleopoda are long and slender, gradually becoming shorter posteriorly ; the 

 terminal pair, which forms the outer rami of the rhipidura, is armed with a strong tooth 

 at about two-fifths from the distal extremity ; the distal division is slightly curved 

 inwards and furnished with many hairs similar to those on the inner margin. 



Telson about half the length of the outer branch of the rhipidura and armed with 

 two short, sharp teeth at the distal extremity, and with three similarly formed articu- 

 lating spines on the lateral margin, of which the anterior is intra-marginal and separated 

 considerably from the posterior two. 



Length, 7 mm. (0-28 in.). 



Habitat. — North of New Guinea (label VI. in Suhm's series). 



Observations. — This species somewhat resembles Sergestes spiniventralis, but differs 

 from it in having no large teeth on the median lobes of the ventral surface of the pleon ; 

 the outer ramus of the rhipidura is broader and armed with a strong lateral tooth, and 

 the telson is longer and armed with lateral spines ; but the most important structural 

 difference appears to me to lie in the distance of the oral apparatus from the cephalic 

 appendages, which is much greater in Sergestes leeviventralls than in Sergestes spini- 

 ventralis. 



Two specimens that correspond with Kroyer's description of Sergestes cornicidum 

 were taken associated with it ; they are both 7 mm. in length. 



Sergestes spiniventralis, n. sp. (PI. LXVII. fig. 5). 



Carapace about one-third the length of the animal. Rostrum long and slender, 

 armed with a slight tooth above and slightly anterior to the frontal margin, which 

 carries a well-developed tooth above the orbit ; antero-lateral angle rounded and smooth. 

 Carapace smooth except for a very small lobe above the mandible and a well-defined 

 tooth in the median line at the posterior margin. 



The first somite of the pleon is dorsally smooth except for a very minute tooth on 

 the posterior margin, and ventrally produced in the median line to a large lobe, that is 

 surmounted by a strong anteriorly directed tooth. The second somite is dorsally armed 

 with a minute tooth on the posterior margin, and ventrally furnished with a strong 

 lobe, surmounted by a strong tooth as in the first somite, but directed downwards. 

 The third somite is dorsally armed with a strong tooth, perpendicular in direction, and 

 ventrally furnished with a large lobe without being surmounted by any tooth. The 

 fourth and fifth somites are similarly armed, but the teeth on the dorsal surface are 

 directed backwards ; and the ventral lobes are less prominent. 



