ATLANT. DEEP-SEA EXPED. 1910. VOL. III.] 



ECHINODERMATA 



39 



Test- 



Number of specimens 



diameter 



Cidaris 



Echinus alexandri. 



Echinus 



acutus. 



in 











millimetres 



Stat. 39 b 



Stat. 88 



Stat. 95 



Stat. 101 



Stat. 23. 



17 



1 



— 











— 



18 



1 



_ 



— 



— 



— 



19 



5 



— 



— 



— 



— 



20 



7 



— 



— 



— 



1 



21 



15 



— 



— • ■ 



— 



— 



22 



23 



— 



— 



— 



— 



23 



28 



— 



— 



— 



— 



24 



15 



— 



— 



— 



— 



25 



13 



1 1 



— 



— 



26 



2 



o 



— 



— 



27 



1 



3 1 



— 



1 



28 



1 



1 3 



— 



— 



29 



— 



2 3 



— 



2 



30 





4 2 



1 



— 



31 





4 



3 



— 



32 



— 



5 1 



4 



— 



33 



— 



13 1 



3 



— 



34 



1 



25 



1 



1 



35 



3 



38 



2 



— 



— 



36 



— 



29 



— 



2 



1 



37 



— 



35 



— 



1 



1 



38 



3 



23 



1 



1 



— 



39 



2 



21 



— 



— 



— 



40 



— 



12 



1 



— 



1 



41 



— 



2 



— 



1 



— 



42 



— 



3 



— 



1 



— 



43 



— 



1 



— 



1 



— 



44 



45 



— 



2 



— 







— 



46 



60 



I 



1 



— 



z 



1 





121 



227 



18 



19 



9 



The material from stat. 95 is very scanty but the exam- 

 ples of Echinus alexandri collected there seem likewise 

 to indicate the presence of more than one year-class at 

 the locality. The specimens of Echinus acutus taken at 

 stat. 101 afford a maximum of 10 individuals at 31 — 33 

 mm., which must represent a year-class. The three 

 individuals at 41 — 43 mm. form another year-class. The 

 grouping of these year-classes can not be definitely 

 determined, however, owing to the scantiness of the 

 material. At stat. 23 three year-classes at least must 

 have been present, as the smallest individual at 20 mm. 

 and the largest at 60 mm. represent one year-class each. 

 The remaining specimens which measured 27 — 40 mm. 

 represent at any rate a third one, but judging from the 

 conditions at stat. 101 I am most inclined to believe that 

 they belong to two different year-classes. At stat. 4 nine 

 individuals were collected of which six measured 62 — 69 

 mm., one 32 mm. and two 10 mm. These three groups 

 must each represent a year-class. 



What has been said above applies also to the 

 Echinothurids. 14 specimens of Phormosoma placenta 

 were taken at stat. 4, 15 at stat. 70, 14 at stat. 101 and 25 

 at stat. 76 A, 1902. Their measurements were as follows: 

 Stat. 4: 60(1), 67(3), 70(1), 72(1) 73(2), 75(2), 77(2), 



79(1), 83(1). 

 Stat. 70: 6(1), 8(1), 9(1), 10(1), 12(1), 14(1), 16(1), 



26(1), 27 (1), 54 (1), 59 (1), 61 (1), 65 (2), 



71 (1). 

 Stat. 101: 44 (1-), 48 (1), 54 (1), 63 (1), 64 (1), 67 (1), 



68 (1), 69 (3), 71 (3), 75 (1). 

 1902, stat. 76 A: 67 (1), 73 (1), 76 (1), 78 (2), 79 (3), 



80 (6), 82 (4), 83 (2), 84 (3), 85 (1), 86 (1). 

 (The numbers in brackets refer to the number of specimens, the others 



to the diameter of the test in millimetres). 



As will be seen stat. 4 afford a maximum of six 

 individuals at 73 — 75 mm, which must represent one 

 year-class, while there is evidently another year-class 

 between 60 and 70 mm. At stat. 70 we find at least a 

 year-class at 6 — 16 mm., another at 26 — 27 mm. and a 

 third gathered about 65 mm., perhaps also a fourth at 

 54 mm. At stat 101 there is a year-class grouped about 

 69 — 73 mm., and the smallest individuals must belong 

 to a different year-class. At .stat. 76 A most of the 

 individuals, are grouped about a diameter of 80 mm. and 

 the smallest specimen must represent a different year-class. 

 Six individuals, taken at stat. 23, show that as many as 

 three year-classes may occur simultaneously in a locality. 

 Their measurements were as follows: 



21, 25, 38, 42, 43 and 74 mm. 



16 specimens of Araiosoma hystrix taken in 1902 by. 

 the "Michael Sars" at stat. 76 A measured: 



35, 85, 89, 96, 97, 98, 99, 102, 106, 108, 112, 131, 

 133 and 146 mm. 



Three specimens measured 102 mm., the remaining 

 measurements included but one individual each. Three 

 year-classes at least of Arceosoma hystrix must hav been 

 found at stat. 76 A, for the largest and the smallest indi- 

 vidual must each represent a year-class, and the third 

 one is grouped about 102 mm. 



Of Sperosoma grimaldii four year-classes at the least 

 were probably present at the same station, as the specimens 

 taken there were of the following dimensions: 



90 (1), 108 (1), 109 (1), 110 (1), 114 (1), 116 (1), 

 122 (1), 123 (1), 127 (2), 143 (2), 145 (1), 153 (1), 154 

 (1), and 188 (1). 



At stat. 88 (1902), there seem at least to have 

 occurred three year-classes, as the specimens measured: 

 75, 94, 105, 132 and 210 mm. respectively. The four 

 Sperosoma grimaldii taken at stat. 25 must likewise have 

 represented three year-classes, as they measured: 73, 

 195, 208 and 220 mm. respectively. 



