LARVAE OF DECAPOD CRUSTACEA 



333 



I have recorded (1924, p. 150) the occurrence of larvae of a species oi Jaxea from 

 New Zealand, and have now found the same form in plankton from Samoa. Two new 

 forms of larva, one of which may belong to a new species of Naiishonia, have been 

 found in the Discovery and Barrier Reef plankton, and they show two steps in the 

 evolution of the elongated head region which is so marked in Jaxea. 



Fig. 34. Upogebia B.R. II. 

 a. Side view. b. Telson. 



Jaxea S. I (Fig. 35) 

 Samoa. 



Stage I. Length 3-55 mm. 



Head region produced into a long "neck", without rostrum; abdomen: somite i 

 with small lateral blunt process, somites 2-5 with sharp pleural hooks. Telson deeply 

 hollowed, with spine formula 7 + 7; spine 2 represented by a small hair not easily 

 seen from above. 



Antennule unsegmented, with inner spine-like process in place of endopod. Antenna : 

 endopod with three long setae, and scale with ten setae ; basis with large ventral spine. 



Left mandible and paragnath sickle-shaped. Maxillule very small, with unsegmented 

 palp and few spines on laciniae. Maxilla with minute lobe representing endopod and 

 four reduced inner lobes ; exopod with only three setae in the specimen examined, and 

 without basal process ; the whole appendage elongated and of three distinct segments. 



Maxillipedes i and 2 with endopod slender, of four segments; exopod with four 

 setae. Maxillipede 3 a small rudiment. 



The larva described by me from New Zealand (1924, p. 150) had a well developed 

 rostrum and rudiments of two pairs of legs, while maxillipede 3 was much larger. It is 

 possible that there are two species differing slightly in degree of development at hatching. 

 The two forms agree in having a pointed lateral process on abdominal somite i which 

 appears to be lacking in J. nocturna. In stage II the New Zealand form has a telson 



