2i6 DISCOVERY REPORTS 



on either side, the second being insignificant and hair-like. The total length from tip of 

 rostrum to the cleft of the telson of the specimen figured was 3-0 mm., considerably 

 smaller than the corresponding size in M. banffica. 



STAGE II (Fig. 2b) 



This is a stage not figured by Lebour (1930) for M. banffica, although described in her 

 text ; it differs from stage I and also from her second larva in the possession of eight 

 spines on either side of the telson. A second and important change is in the spinulation 

 of the postero-dorsal margins of the abdominal segments. The postero-dorsal margin of 

 the first segment is now smooth, whilst only the four large spines remain in this position 

 on the second to fifth segments. The strong lateral spines persist on the fourth and fifth 

 abdominal segments. On each segment bearing dorsal spines small hairs arise slightly 

 anterior to the base of the outer of these spines. The antennal scale now carries nine 

 plumose hairs instead of eight, and the antennule is composed of two segments. The 

 shape of the carapace has become modified, giving the eyes greater prominence, and the 

 importance of the fourth spine of the telson is foreshadowed in its increasing size. The 

 total length of the specimen figured was 4-0 mm. 



STAGE III (Fig. 2a) 



The division of the sixth abdominal segment from the telson and the appearance of 

 the uropods mark a strong advance in the development of the larva. The number of 

 spines on either side of the telson is increased to nine, the fourth equalling the first in 

 size and now fused with the telson. The outer branch of the uropod carries ten plumose 

 hairs, the inner branch being still non-setose. The sixth abdominal segment carries 

 a stout mid-dorsal spine only. The dorsal spines of the preceding four segments are 

 reduced in size, the fourth segment carrying the largest. The hairs on the antennal scale 

 are increased to ten. The prickles previously present on the tip of the rostrum, on the 

 tips of the antennal scales and on the tips of the first spines of the telson have disap- 

 peared. The total length of the specimen figured was 5-5 mm. 



STAGE IV (Fig. 36) 



A great reduction in the size of the outer spines of the telson, the fourth now being 

 predominant, and an increase in the total number to eleven, mark this stage. The inner 

 branch of the uropod carries seven plumose setae and the terminal seta of the outer 

 branch has become spinose and fused. The second abdominal segment has lost all 

 spines, and those on the postero-dorsal margins of the third to the fifth segments are 

 again reduced in size. The proximal segment of the antennule has lost the stout seta it 

 previously carried and this has been replaced by one arising lower down. The distal 

 segment of the antennule carries more aesthetes on its inner side. The number of hairs 

 on the antennal scale is again increased and is now fifteen. The number of teeth on the 

 posterior margin of the carapace is reduced. The total length of the specimen figured 

 was 8-0 mm. 



