ACTINOMETRA ROUUÜTIPINNA. 201 



spiny pinnules. As in the » Challenger" specimen and in von 

 Rosenberg's large one from Jobie four of the primary arms 

 consist of but two distichal joints which are united by syzy- 

 gy as in the later arm-divisions ; and it is quite possible 

 that specimens may eventually be met with which have 

 more than half the primary arms in this condition. Variat- 

 ions of a similar character are common in other Actino- 

 metrae and notably in Act. porvicirra but the arm-divisions 

 of Antedon are generally much more regular. 



Act. typica is the nearest ally oï Act. Novae Guitieae , hui 

 the metamorphosis of the centrodorsal is carried much fur- 

 ther than in that type, it being markedly stellate in shape 

 and bearing few or no cirrhus-sockets. In Act. Novae 

 Guineae, on the other hand the centrodorsal bears some 15 

 functional cirrhus-sockets and presents but little departure 

 from the ordinary shape. The joints of the terminal pinn- 

 ules in Act. typica also are much longer and more slen- 

 der than those of Act. Novae Guincae , which are compara- 

 tively stout and but little louger than broad. They are 

 also peculiar in having the large lateral spines almost en- 

 tirely limited to the outer side of each joint , instead of 

 occurring on both sides as in Act. typica. 



14. JËctinometfa robustipinnu, u. sp. 



Description of a much mutilated individual. 



Centrodorsal a thick disc slightly flattened at the dor- 

 sal pole , and bearing about 40 cirrhus-sockets in two mar- 

 ginal rows. First radials partially visible all round the 

 calyx, but slightly diverging at each angle so as to leave 

 a gap. This is bridged over by the proximal portions of 

 the short second radials having lateral extensions which 

 meet those of their fellows on either side. Axillaries pen- 

 tagonal , quite free laterally, and rather more than twice 

 the length of the second radials , with moderately sharp 

 distal angles. Rays may divide three times; 17 -f" arms. 

 Six of the primary arms consist of three distichal joints , 



]>f otes froiTi the Leyden IMuseum , Vol. III. 



13 



