48 CLEVB, PLANKTON FROM THE INDIAN OCEAN AND THE MALAY AECHIPELAGO. 



Masticatory apparatus of the mandihle well developed, with 1 small Si and a row 

 of teeth, which are raore acute towards the interiör margin. Exteriör tooth large, sepa- 

 rated by a gap from the others. 



Maxilla. B 1 as long as broad and as 5 2 and Ri together. Li 1 ^/s as long as iJ 1, 

 convex, with about 10 strong bristles, some of which are pluinose. The proximal has 

 the same length as the lobus. L 2 and L 3 small, each with 3 -S. B 2 longer than 

 broa.d, with 4 ;S at the distal interiör end. Ri half as long as i? 2 and as Ee, with 

 rndimentary articulation ; its S: 4 -j- 4 -f- 7. Re not articulating with i? 2. Its distal end 

 reaches beyond B 2 or nearly to the end of Ri; its S 10. 



First inaxillipeds well developed, 3 times longer than broad. Lobes digitiform, 

 crowded. L 1 with 4 (.5?) longer and 1 short S, L 2 — L 4 with 2 long and 1 short »S'. 

 L 5 with 2 long and 1 short »S(?). Ri with 5 stronger and 2 finer S(^)- 



Second maxilliped. B 1, B 2 and Ri of about equal length. B 1 and B 2 somewhat 

 more than twice as long as broad. S of i) 1 : 2, 3, 4. B 2 ^vith 3 central and 2 distal S. 

 Ri 1 and 2 with 3, Ri 3 and 4 with 2 Si. Ri 5 with 3 Si. Ri 4 and 5 end with 1 

 plumose Se. 



Natatory legs 1 — 4. B 2-jointed; Re 3-jointed; 7?/ of the 1st p. 2-jointed, of the 

 other 3-jointed. Proportional length of B and Re 5 : 6 on the 1st p., about 1 : 2 on the 

 other. Ri of the 1st p. about half as long as Re; of the other from 'Vs to ^/2 as long. 

 B 1 with straight margin and 1 plumose Si reaching to the distal margin of i> 2. B \ 

 and B 2 naked, but B 2 of the 1st p. with a curved Si. Re 1 of the 1st p. as long as 

 Re 2, and Re 3 as long as Re 1 and 2 together. Re 1 of 2nd — 4th p. shorter than Re 2. 

 Re 3 about as long as Re 1 and 2 together. Re 1 of the 3rd p. and Re 2 of the 2iid 

 and 3rd p. with some spines on the flat surfaces. Se of the 1st p. O, O, 2, of the other 

 1, 1, 2. aS^ of the 1st p. bristle-iike, of the other somewhat shorter than Re 3, knife-like, 

 with entire exteriör margin. Si of the 1st p. 1, 1, 4, of the other 1, 1, 5. & 3 of the 

 2nd — 4th p. divides Re 'd in a distal and a proximal part, the latter being IV2, 2, 4 

 times longer than the former and on the exteriör margin, saw-like. Ri 1 of the first 

 pair somewhat shorter than Ri 2, of the other pairs very short. Ri 1 of all pairs with 

 1 Si; Ri 2 of the 1st p. with 5 S. Ri 2. of the 2—4 p. with 2 Si and Ri 3 with 7 5. 

 Surface of Ri 2 of the 2iid to 4th p. ^vith several sets of spines. 



Fifth i^air of legs asymmetrical, the left being longer and 4-jointed, the right half 

 as long and 3-jointed. 



It is apparent from the above description, that the sexual differences are far from 

 being as marked in P. aculeatus as in P. parvus. 



Pseudodiaptomus Aurivillii Cl., n. sp. 



(Pl. VI, %. 11—22; Pl. VII, fig. 1—2). 



Diagnosis of the female. Th 1 and Th 2 uniting; last segment of the thorax 

 ending (laterally) in a spine; posterior margin of the thoracic segments smooth. Abdomen 

 4-jointed. Posterior margin of the 3 first abdominal segments with a roAV of small tri- 

 angulär scales. Antennii3 of the 1st pair 20-jointed. St of the furca of equal thickness. 



