DEVELOPMENT OF E. SPINIFERA 299 



frontal plate is different in each of the three specimens : in one it is as in the previous 

 stage ; in another it is similar except that the anterior margin is nearly straight ; in the 

 third it is square with its anterior margin almost straight and with a tiny spine in the 

 centre — the beginning of the rostrum.^ 



In one there are a few denticles on the lateral margin of the carapace by the antero- 

 lateral spines, but in the other two there are none. The posterior projection of the 

 carapace is strong, as long as the first and second abdominal somites. 



The antennular spine is as long as the sum of the second and third peduncular seg- 

 ments ; the flagella are of the same length and beginning to segment. 



The thoracic limbs of the specimen ca. 6-5 mm. long are as follows: 



Second limb. Endopod of five segments and feebly kneed. A gill of two branches. 



Third limb. Endopod much shorter than that of second, of five segments and feebly 

 kneed. A gill of two branches. 



Fourth limb. Short, the endopod of three indistinct segments, setose. A gill of two 

 branches. 



Fifth limb. A small bud about to bifurcate and to bud off a gill. 



Sixth limb. No free bud. 



Seventh limb. A single gill bud. 



Eighth limb. No free bud. 



The spine of the third abdominal somite is very strong, half or more than half as long 

 as the fourth somite. The posterior margin of the telson carrying the seven terminal 

 spines is considerably narrower than in the previous stage. The middlemost of the three 

 postero-lateral spines is still the longest ; the innermost is thickening or very thick. 



Furcilia, stage IV (Fig. 40/) 



Description based on the examination of six specimens. One is 6-o, two are 6-4, and one each 

 6-5, 6-7 and 6-8 ram. long. 



In this stage there are five pairs of setose pleopods and an unsegmented antennal 

 endopod. 



The dorsal organ may be conspicuous but not high, or a low crest. In one specimen 

 the frontal plate is large and square with rounded corners, nearly parallel lateral mar- 

 gins, an emarginate anterior margin and its edges beset with denticles, but with no 

 beginning of the rostral spine. In the other five it is as above except (i) that in two it is 

 wider at the end than at the base so that the lateral margins are not parallel, (ii) that the 

 anterior margin is only feebly emarginate or nearly straight and has at its centre a spine, 

 the beginning of the rostral spine, standing well out beyond the denticles. In five of the 

 specimens the posterior projection of the carapace reaches halfway or more down the 

 second abdominal somite ; in the sixth it is only half the length of the first somite. 



The antennular spine may be longer or shorter than the sum of the second and third 

 peduncular segments. The flagella are long and segmented. 



1 Note that although this spine may be present in this stage it may be absent in the next. 



