238 W, M. Tattersai,!^ : Two new MysidcB. [Voi<. 11^ 



Eye. — In M. orientalis the eye is only 9 per cent, of the total 

 body-length, is very little more than twice as long as broad at the 

 cornea, and the latter occupies the distal third of the whole eye. 

 In M. slabberi the eye is 17 per cent, of the total body-length, is 

 three-and-a-half times as long as broad, and the cornea occupies 

 the distal two ninths of the whole eye. So that in M. orientalis 

 the eye is on the whole very much shorter than in M. slabberi. 



The antennular peduncle in M. orientalis is considerably shorter 

 than in M. slabberi, being only 11 '8 per cent, of the total body- 

 length in the former compared with i8'6 per cent, in the latter. 

 The shortening of the antennular peduncle in M. orientalis is pro- 

 portional to that of the eye, so that in both species the eye bears 

 the same relation to the antennular peduncle^ i.e.^ it extends to 

 about the distal end of the second joint. The spine-like seta on 

 the outer distal corner of the basal joint of the antennular peduncle 

 is scarcely as robust in M. orientalis as in M. slabberi. 



The antennal scale is of practically the same size in both species, 

 with the result that, owing to the shortening up of the antennular 

 peduncle in M. orientalis, the scale extends beyond the antennular 

 peduncle, while in M. slabberi it falls short of it. 



Telson. — The telson of M. orientalis (fig. 7) differs from that 

 of M. slabberi mainly in having the serrated apical portion more 

 produced and the whole telson consequently proportionally longer. 

 The serrated apical portion of the telson in M. slabberi is only 

 about one quarter of the entire length of the telson, whereas 

 in M. orientalis it is considerably more than one third of that 

 length. 



In the structure of the various appendages the two species 

 show considerable resemblance, but minor differences are to be 

 noted. For this purpose I give, on pi. xxii, figures of the various 

 appendages of M. orientalis for comparison with those of M. 

 slabberi. 



In the second thoracic limb of M. orientalis (fig. 5) the ter- 

 minal joint is somewhat longer and narrower than in the same 

 limb of M. slabberi. The number of joints in the tarsus of the 

 third to the eighth thoracic limbs of M. orientalis varies from five 

 to nine, the eighth limb usually having fewest joints in the tarsus. 

 Thus in one female example dissected the joints of the tarsus were 

 seven in the third, fourth and fifth limbs, eight in the sixth, nine 

 in the seventh and only six in the eighth. Figure 6 depicts the 

 eighth thoracic limb of a male with only five joints in the tarsus. 



The fourth pleopod of the male of M. orientalis differs rather 

 markedly from the same appendage in M. slabberi, in having the 

 first joint of the outer ramus shorter than the entire inner ramus. 

 In M. slabberi the reverse obtains. Otherwise the appendages in 

 question are very similar. 



I could not detect any spine on the inner ventral margin of the 

 inner uropod of M. orientalis such as exists in M. slabberi. 



Length of the largest specimens of M. orientalis, both males and 

 females, 7 mm. from the rostrum to the apex of the telson. 



