DEVELOPMENT OF EUPHAUSIA SUPERB A 69 



Sixth Furcilia (p. 96). One terminal spine on the telson, postero-lateral spines not 

 reduced in number. 



This account excludes description of larvae with six-, four-, or two-spined telson; 

 these are rarely occurring aberrant forms which in development are intermediate be- 

 tween those larvae whose telson spine numbers are respectively one greater and one less. 

 Tables giving particulars of these forms are inserted in their appropriate positions. 



FIRST FURCILIA 

 Included in this stage are the following larvae in advance of the 3rd Calyptopis: 



(a) Larvae with no pleopods. 



(6) ,, I pair of non-setose pleopods. 



V') It 2 ,, ,, ,, 



{d) .. 3 



(e) >. 4 



(/) .. 5 



All these forms, with the exception of (6), are represented in the material examined. 



In Table XXIX the non-setose larvae have been separated into groups according to 

 the number of pleopods. At the end of each subdivision the number of larvae, their 

 range of size and average length are stated. An examination of the number of larvae 

 recorded in each subdivision demonstrates the dominance of the {e) and (/) forms, 

 particularly the latter, and the comparative rarity of the others. It will be noted that 

 there is a direct correlation between the number of pleopods and the average sizes in 

 the different groups. 



For all the ist Furcilia the average length is 5-30 mm., and the range is from 3-50 to 

 6-50 mm. 



Larvae having two, three, four and five pairs of non-setose pleopods were examined 

 in detail. 



The eyes project beyond the edge of the carapace which has two emarginations an- 

 teriorly between which is the rostral plate (Figs. 15^, h,j). In the two-pleopod form 

 the anterior edges of the rostral plate form a very obtuse angle, but in the larvae with 

 more pleopods the rostrum is evenly rounded, reaching not quite to the distal margin 

 of the basal antennular segment in the smaller larvae and still more distant from it in 

 the larger larvae. The smaller larvae have no spine on the postero-lateral margin of the 

 carapace ; it is present, but inconspicuous, in the larva with four pairs of pleopods and is 

 quite a distinct denticle in the largest larva in this group (Figs, i^ a, b, c). 



The telson (Figs. 15 </, e) is seven-spined terminally, has three postero-lateral spines 

 and a spine situated laterally on each side about the middle of the telson length. The 

 seven terminal spines have spinules on each lateral edge ; the postero-laterals bear them 

 on the inner edge and less obviously dorsally. Both lateral and postero-lateral spines 

 have a somewhat larger spinule than the rest situated dorsally at some distance from the 

 tip. The telson length is more than twice the width except in the smallest larvae in which 

 it is a little less. 



