HELIOMETRINAE 



143 



Bernasconi's five drawings show the anterior primary furrow supplying only one pair 

 of arms: it does so in seven of my specimens. 



It appears that some of the primary ambulacral furrows divide in a less variable way 



than others. 



Side plates and spicules. Clark(i9i5 «, p. 132) thinks thatthe presence of well-developed 



plates is a sign of immaturity, and that poorly developed plates, or the absence of plates, 



is characteristic of mature individuals. I do not find it so in this collection. But there is 



a relation between locality and the presence or absence of well-developed plates : it is 



shown by the following table: 



It is not only a question of numbers : the degree of plating varies as well. Of the 

 seven specimens with plates from the west coast of Graham Land five are heavily plated ; 

 of the twenty-nine from the Bransfield Strait at least thirteen are heavily plated. The six 

 specimens having plates from the South Sandwich Islands all have very small ones (the 

 size of the largest is shown in Fig. 2b): m three of them the greatest number of plates in 

 one pinnule is two, and they are minute and near the tip. In the five specimens from 

 South Georgia possessing plates they are as small as, or smaller than, those of the South 

 Sandwich specimens. In three of them there are two or three very reduced plates near 

 the tips of some pinnules but none in others. So it is probable that if a larger number 

 of pinnules of every South Georgia specimen were examined the proportion of indi- 

 viduals with plates would be found to be higher: but they would be very small plates, 

 few in number and unevenly distributed. It is, at least, quite certain that none of the 

 South Georgia specimens has even moderately developed plates ; nor were spicules seen 

 in the tentacles of any. 



Although the South Sandwich specimens have plates nearly as small as those from 

 South Georgia, two of them do have spicules in the tentacles as well and so, in this way, 

 stand intermediately between the South Georgia population and that of the Bransfield 

 Strait and the west coast of Graham Land where most of the specimens with plates 

 have spicules too. 



From these facts it would appear that in this sector of the Antarctic the Promacho- 

 criiius kerguelensis living in lower latitudes are most often without plates and always 

 devoid of spicules, but that a small proportion have very reduced plates, few in number, 

 on at least some of their pinnules ; that the majority of those living in high latitudes have 



