1922.] W. M. Tattersat.l : Indian Mysidacea. 453 



beyond half way down the uropods, one and a half times as long as 

 broad at its base, proximal portion of the lateral margins with two 

 or three spines, apex broadly truncate or even slightly emarginate, 

 its breadth equal to half the total length of the telson ; distal 

 portions of the lateral margins and the apex together bearing about 

 five or six pairs of spines, the innermost pair of spines at the apex 

 equal in length to three quarters of the breadth of the apex, 

 the remaining spines grading smaller in size, the fifth and sixth 

 spines quite small. The centre of the apex bearing the usual pair 

 of plumose setae which are longer than the innermost spines, and, 

 hidden in dorsal view but visible under the high power of the 

 microscope (£) in ventral view, are three very small spinules, cor- 

 responding to the three small spines usually present in that posi- 

 tion, but greatly reduced in size and at first sight apparently absent. 

 Uropods about twice as long as the telson, the endopod slightly 

 shorter than the exopod, with a row of 10-12 spines along the 

 entire margin, regularly graded in size with no smaller spines 

 between; proximal joint of the exopod about three times as long 

 as the distal, with a group of five spines at the distal end, the rest 

 of the margin naked, distal joint about as long as broad. Pseu- 

 dobranchial rami of the second to the fourth pairs of the pleopods 

 of the male spirally twisted. Third and fourth pairs of male 

 pleopods with the endopod and exopod subequal in length and 

 having a normal armature of plumose setae, none of which are 

 modified. Length of adult males and females 6 mm. 



This species falls into Hansen's group I, characterized by the 

 spiral \y- twisted pseudobranchial rami of the second to the fourth 

 pleopods of the male and the unmodified nature of the setae on 

 the terminal parts of these pleopods. It is distinguished sp?cially 

 by the very short telson and its peculiar armature of spines and 

 by the very reduced size of the three spinules at its apex between 

 the innermost long pair of spines. 



It has been a source of great satisfaction to rediscover 

 Paulson's species and to find that it is a good species which its 

 original discoverer described and illustrated adequately. The 

 species was quite easy to recognise from Paulson's figures, but 

 in view of the rarity of his work I have thought it well to 

 redescribe and figure it here and to indicate its true position in 

 the light of recent work. As far as I can make out Hansen's 

 group I contains at present about 12 species. Of this group S. 

 thompsoni and 5. gracilis differ from the rest in having the endopod 

 of the uropods longer that the exopod. The four species S. 

 clausii, S. 'jaltensis, S. norvegica and 5. brookii are distinguished 

 from the remainder in having more than half of the outer margin 

 of the proximal joint of the exopod armed with spines. The 

 remaining species in this group are S. quadrisfiinosa, S. nodosa, 

 S. vulgaris, S. afjlnis, S. watasei and S. hngipes (the last two doubt- 

 fully placed here), and 5. brevicaudata is most closely allied to the 

 two first-named forms. 



Distribution. — Known previously only from the Red Sea. 



