Arctic and North-Athnlic Starfishes. 105 



first locality and the largest from the last-nauied one must be 

 of nil age othor than the rest. 



I stated above that the examples of Pontaster tenuisptnus 

 examined represent thice or pos.><ibIy four annual classes. 

 The material of Ctenoiit.scun crixjmtus is only comj)osod of 

 three ycar-classL-s : 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 l.^-IG mm. A fourth year-class seems to bo out of 

 the question in the case of tliis species, as it has already 

 attainetl its maximum growth at 18-19 mm. 



It has been mentioned already that the food-conditions and 

 then-fcne the conditions of growth may be dilTerent in different 

 lociilities. The maximum o£ a year-class will be gathered 

 about a measuiement which vaiies somewiiat for different 

 localities. In speaking of Pontaster tenuispinus I have called 

 attcTition to this fact, wliich 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, 

 wliich has evidently offered the best conditions of life. I 

 ou;;ht to mention that the material from all localities was 

 collected in June, though in different years. 



As it is with these two si)ecies, so it is with others that 

 live at shallower depths in Arctic and boreal waters. The 

 conditions are the same sit the great depths in the Norwegian 

 iSea and the North Atlantic. The * Michael Sars ' took 2^ 

 Ilyinenuster pellucidus in 1900 in the cold area off the east 

 coa>t 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 

 Koiwegian Sea is Jiuthyhiaster vexillifer, which may also bo 

 lej resented by seveial year-classes at a locality. It may 

 be nientioned that the juvenile specimens of Bath y blaster 

 v^.riUifer, described by Danielsst-n and Koren under the name 

 Jli/ut>ter inirahilisj Wits taken together with two full-grown 

 oiifs. 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 measurrd 4 nnn., another of 7 mm., and 

 still others of as much as 22 mm.; some of these were thus 

 jimong the largest known in this species. In other words, 



Ann. ^l:: Ma^. y. H'-' S, r \\ I'./, iii. 27 



