124 Mr. C. Chilton on a new Species ofldotea. 



sixth. First segment produced into rounded antero-lateral 

 lobes, which reach to the eyes. Two raised ridges, one near 

 each lateral border, run throughout the whole length of the 

 thorax, and extend nearly to the end of the postabdoraen. 

 There is also a less perfect median ridge formed by the poste- 

 rior portion of each segment being raised into two short 

 converging ridges, like the letter V ; this ridge is well 

 marked in the postabdomen and extends right to the end. 

 Between the lateral ridges and the median ridge, but nearer 

 to the former, are various sculptured markings. Postabdomen 

 about as long as the five preceding segments of the thorax, 

 composed of three distinct segments, the first two short, the 

 third with the lateral sutures of another segment. Post- 

 abdomen gradually narrowing until about one third of its 

 length from the end, when it suddenly contracts and con- 

 verges with slightly sinuous margins to the extremity, which 

 is subacute. Eyes small, situated on the lateral margin of 

 the head at the postero-lateral angle. Antennas reaching 

 nearly to the end of the third segment of the peduncle of 

 the antennule ; penultimate segment expanding distally, ter- 

 minal segment very small. Antennules as long as the head 

 and first two segments of thorax ; last segment of peduncle 

 longer than the preceding, but slightly shorter than the fla- 

 gellum, which is composed (in my single specimen) of seven 

 joints, of which the first is considerably longer than any of 

 the succeeding. Epimera of only the last three segments of 

 thorax visible in dorsal view ; in side view they are all rectan- 

 gular, those of second and third segments not reaching to the 

 anterior end of the epimeron of succeeding segment. Oper- 

 cular plates subtriangular, with slightly raised border on inner 

 margin ; terminal plates very small, triangular, ending acutely. 

 Legs short, not visible in dorsal view. Colour greyish. 



Length 10 millim. ; breadth (about) 4 millim. 



Hob. Sumner, Canterbury, New Zealand. 



A single specimen, taken on the under surface of a boulder 

 exposed at low tide. 



EXPLANATION OF PLATE V. A. figs. 1-3. 



Fig. 1. Idotea f estiva, dorsal view, X 10. 



Fig. 2. The same, side view, X 10. 



Fig. 3. The same, opercular plates, X (about) 13. 



