Archet. — The Marine Crayfish of New Zealand. 



403 



(c.) The Pueriflns. 



The puerulus is, at first siglit, simply a small adult, and, indeed, some 

 of these larval forms have been described as species of a genus Puerulus 

 Ortmann (1897, p. 290, footnote). Dr. Caiman (1909, p. 441) is of the 

 opinion that this genus is a perfectly valid one, the species of which are 

 really quite distinct from the puerulus larva. The characters which can 

 be recognized as larval characters are the presence of vestiges of exopods 

 on the thoracic limbs, the absence of the cervical groove, the separation 

 of the 3rd maxillipedes at their base, the carapace having few spines and 

 having lateral ridges giving it a prismatic instead of a cylindrical form. 

 More important is the presence, at the end of the appendix interna of the 

 pleopods, of small coupling-hooks, which enable the pleopods to be joined 

 together in pairs, and thus to make efficient swimming-organs. 



The specimens which I have are undoubtedly pueruli, those from Stewart 

 Island being 30 mm. in length, and that from Cuvier Island 20 mm. There 

 are certain differences between the Cuvier Island specimens and those from 

 Stewart Island, such as leave no doubt in my mind that the Stewart Island 

 forms are pueruli of Jasiis lalandii, while the Cuvier Island puerulus is the 

 larva of J. hUgelii. For instance, the rostra show exactly the differences 

 which have been set down above in the key to the species, that of the 

 Cuvier Island puerulus being as large as the supra-orbital spines, and pro- 

 jecting straight forward, while the larvae from Stewart Island have a small 

 rostrum, bent down towards the antennules and slightly turned up at 

 the tip. Certain details of the spinulation of the telson mark further 

 dift'erences, the large spines in the Stewart Island larvae being placed exactly 

 as in the adult J. lalandii, while in the Cuvier Island larvae there is a 

 distinctly different pattern, which, though not arranged exactly as in the 

 adult J. hiigelii, certainly tends towards that arrangement. 



Fig. 4. — Puerulus of Jasus lalandii (M.-Edw.), Stewart Island. X 3. 



Puerulus of Jasus lalandii (M.-Edw.) (fig. 4). 



Carapace with lateral ridges giving it a somewhat prismatic form, wider 

 posteriorly than anteriorly ; spines very few, but, where present, distinct. 

 Cervical groove very indistinct ; supra-orbital spines large, projecting up- 



