Arctic and North-Atlantic Starfishes. 405 
first locality and the largest from the last-named one must be 
of an age other than the rest. 
I stated above that the examples of Pontaster tenuispinus 
examined represent three or possibly four annual classes, 
The material of Ctenodiscus crispatus is only composed of 
three year-classes : the maximum of the youngest class is at 
4—5 mm., that of the second at about 10 mm., and that of the 
third at 15-16 mm. A fourth year-class seems to be out of 
the question in the case of this species, as it has already 
attained its maximum growth at 18-19 mm. 
It has been mentioned already that the food-conditions and 
therefore the conditions of growth may be different in different 
localities. ‘The maximum of a year-class will be gathered 
about a measurement which varies somewhat for different 
localities. In speaking of Pontaster tenuispinus I have called 
attention to this fact, which is still more striking when we 
compare the material of Ctenodiscus crispatus mentioned 
above. As will be shown below, the two-year old annual 
class has its maximum at a disc-radius of 7-10 mm. at one 
locality, at 8-11 mm. at another, and at 9-12 mm. at a third, 
which has evidently offered the best conditions of life. I 
ought to mention that tle material from all localities was 
collected in June, though in different years. 
As it is with these two species, so it is with others that 
live at shallower depths in Arctic and boreal waters. The 
conditions are the same at the great depths in the Norwegian 
Sea and the North Atlantic. The ‘ Michael Sars’ took 26 
Hymenaster pellucidus in 1900 in the cold area off the east 
coast of Iceland with a disc-radius of 4-25 mm. This 
material affords a maximum of 9 specimens at 8-9 mm., 
fewer at 14-15 mm., and still fewer at 22 mm.; there were 
thus three year-classes from this locality. Other material 
indicates that the 4 mm. specimens represented a fourth 
annual class. 
Another species characteristic of the cold area of the 
Norwegian Sea is Bathybiaster veaillifer, which may also be 
represented by several year-classes at a locality. It may 
be mentioned that the juvenile specimens of Bathybiaster 
vevillifer, described by Danielssen and Koren under the name 
Liyaster mirabilis, was taken together with two full-grown 
ones. The ‘ Michael Sars’ found in 1902 at a locality in the 
cold area north of the Faroe Islands a very young specimen 
whose disc-radius measured 4 mm., another of 7 mm., and 
still others of as much as 22 mm.; some of these were thus 
among the largest known in this species. In other words, 
Ann. & Mag. N. Hist. Ser, 9. Vol. iii. 27 
