Archey. — Fresh-water Crayfish of New Zealand. 



299 



III. Nature and Arrangement of the Spines on the Carapace (fig. 2). 



A. Two sharp spines always present. 



B. Average number 5, present in specimens 60min,. or more in length. 



C. Increase in number according to the size of the specimen, up to 5 



or 6. 



D. Varv in number with the size of the specimen ; they are sometimes 



situated on a slight ridge on the carapace. 



E. One or 2 (very rarely 3), on a distinct ridge. 



F. Present only in large crayfish ; usually 3 in number. 



G. These spines vary in number from to 6, in accordance with the 



size of the specimens. Specimens about 80 mm. long have either 

 3 or 4. 



Fig. 2. — Carapace of P. planifrons, showing arrangement of opines. 



H. This group varies in number from 4 to 13, independently of size, sex, 



or locality : 7 and 9 are most commonly found. 

 J. The anterior portion of this region is armed with spines, merging 



into small rounded tubercles posteriorly. 

 K. Present in the larger specimens only ; usually 3 or 4 in number, 



but 11 have been found here. 



IV. Total Body Length -r- Rostrum Length (column 4). 



The usual specific proportion is 6*5. The Hawke's Bay and Napier 

 specimens have a slightly longer rostrum (average proportion, 5-96), and 

 the Wellington and north-east Marlborough specimens have a very short 

 rostrum (proportion, 7-1) — shorter, indeed, than in P. setosus. 



V. Rostrum Length -r- Rostrum Breadth (column 3). 



There is not much definite variation correlated with definite localities, 

 but the rostrum of crayfish from south of Wellington (inclusive) is con- 

 siderably wider than that of those in the north. There are individual 

 exceptions to this rule — e.g., D'Urville Island and Spring Creek specimens 

 have a narrow rostrum, while the Rotorua specimens have a wide one ; 

 but generally the proportion is the same. 



