304 Transactions. 



II. Nature of the Spines of the Carapace. 



The carapace of P. setosus is covered with sharp, forwardly directed 

 spines, which can he arranged in the same reference groups as in P. plani- 

 frons. The arrangement of the spines is exactly the same in P. zealandicus 

 as in P. setosus, but in P. zealandicus rounded tubercles take the place of 

 the sharp spines. The following account of the arrangement of the spines 

 will be equally applicable to the two species. 



III. Arrangement of the Spines on the Carapace, P. setosus and P. zealandicus. 



A. Constantly 2 in number. 



B. Increasing in number according to the size of the specimen. In 



moderate-sized individuals the number is from 6 to 8. 



C. Usually 4 or 5, appearing first in specimens of 50 mm. length. 



G F J K 



Fig. 7. — Carapace of P. setosus, showing arrangement of spines. 



D. There are generally from 10 to 12 spines here ; they are first de- 



veloped in specimens 50 mm. long. 



E. A ridge on the carapace in this region bears 1 or 2 spines ; occasion- 



ally a third is developed. 



F. Five or 6 is the greatest number found here ; they appear only in 



the large specimens. 



G. This group is constant in specimens of 50 mm. or more in length. 



The spines, which are very distinct, are usually 3 or 4 in 



number. 

 H. Five or 6 spines appear here in specimens 40 mm. long ; the usual 



number in ordinary-sized individuals is 8. 

 J. These are quite distinct and fairly numerous just behind the cervical 



groove, but become fewer and less distinct posteriorly. 

 K. These spines are not often present, and do not appear in specimens 



under 90 mm. long. When present, there are only 4 or 5 de- 

 veloped. 

 L. This is a large group, varying considerably in number. The usual 



number for moderate-sized specimens is 10-12. 



