160 THE IIO\. PAUL A. METHUEN ON [Feb. 1, 



Genus Metabiaptomus (gen. n.). 



Diagnosis. Both antennules of female and left of male consist 

 of twenty-six segments. Proliferation to form this extra joint 

 has not apparently taken place in the same manner as in Adiaptomtis 

 judging from the explanation and figure given by A. W. Cooper 

 (loc. tit.). In the sixth pair of thoracic limbs in the male, the 

 exopodite of the right appendage is three-jointed ; the basipodite 

 is much enlarged on the internal surface to form a double cushion. 

 The first joint of the two-jointed exopodite of the left leg carries 

 a large curved claw, and distally two cushion-like processes are 

 present. An endopodite to this left appendage appears to be 

 wanting, but it may be present in a very reduced condition. 



In other respects like the genus Diaptomus. 



Metadiaptomus transvaalensis, sp. n. (PI. XVI. figs. 46 a-c, 

 & Pis. XVII. & XVIII.) 



Description of female.— Length of cephalothorax l'25mm.; of 

 abdomen including furcal bristles - 7 mm. : of antennule 1"27 mm. 

 Body subcylindrical, the greatest breadth at the junction of the 

 third and fourth segments ; the anterior portion of the body 

 shaped like the nose of a bullet ; the posterior part tapers 

 slightly. The cephalothorax is composed of six distinct segments, 

 the antennal region being distinctly divided from the rest of the 

 body ; the sixth segment bears projecting angular corners on its 

 marginal lobes ; these corners do not seem to represent another 

 segment. The antennules when flexed back in line with the body 

 do not extend beyond the limits of the cephalothorax. The 

 abdomen consists of three distinct segments and the caudal rami. 



Description of male. — Length of cephalothorax "8 mm. ; of 

 ahdomen, as for female, *45 mm. ; of left antennule - 86 mm. 

 The great difference of size between the male and female is to be 

 remarked upon. In general shape however and in its appendages 

 it resembles the female. The abdomen consists of five segments 

 and the caudal rami. The light antennule is geniculated. 



Appendages. — The descriptions and drawings of the appendages 

 have been taken in nearly all cases from females. 



The antennules of the female and the left one of the male are 

 made up of twenty-six distinct segments, a feature of Adiaptomus 

 (see introduction p. 150). It is to be noticed, however, that 

 whereas the proximal spine on the antennule of a female 

 Adiaptomus occurs on the third segment, in that of Metadiaptomus 

 it occurs on the second. From this evidence alone, it is concluded 

 that proliferation to form this additional segment has not taken 

 place in the same area or rather in the same way as in Adiaptomus 

 as explained by A. W. Cooper (loc. cit. p. 101 and figs. 5, 5 a). 

 Xow, from the sudden change of length exhibited in segments 

 twelve and thirteen, it is tentatively suggested that proliferation 

 may have taken place from a segment once representing segments 

 eleven and twelve (ride PI. XVII. fig. 47). This explanation 



