634 Transactions. 
and only slightly produced ; fourth, fifth, and sixth pleon segments very 
small. (Fig. 1. 
yes of moderate size, rounded, black. | 
posterior or inner margins. (Fig. 2. 
Second antenna slender and longer than first, sharply bent backwards 
at end of first visible joint, which probably represents the third peduncular 
joint and is longer than the next two together, penultimate joint curved 
at base, about three-fourths as long as last joint of peduncle; flagellum — 
six-jointed, about as long as last two joints of peduncle. (Fig. 3.) > 
7 
Tetradeion crassum Chilton. 
Fic. 6.—First maxilla; outer lobe Fic. 7.—Second maxilla. 
seen in profile. | Fic. 8.— Maxilliped. 
The mouth-parts prove to be very similar to those of Phippsia gibbosa 
and in both genera have probably hs modified in correlation with the 
enormous development of the side-plates and the habits of the animal 
arising in connection therewith. zm 
Mandible slender, elongated, nearly straight, cutting-edge formed 
about six or seven short teeth; inner eutting-edge, spine row, mo 
tubercle, and palp entirely absent unless а long seta on the outer surface 
represents the palp. (Fig. 4.) 
