KCHINODERMS. 

 Percentage of magnenum carbonate in sea urchins. 



25 



Ivhiiuis -.■••.■■■ 



Siiiim;yIo(entrotusdr6l)achiensis. 



Ti'trapyt;iis 



Ei-hinarachuius 



Stron.aylocontrolus fnigilis 



Loxpcliinus 



("lypeivsfer 



I.ytcchinus 



Trctocidaris 



Kiiropp falil'ornica 



Kchiiiomotra 



yU>\\\i■^ 



Hotoroceiitrotus. .. 

 Encope inicropora. 



Loralitv. 



Slation 2206... 



(JroonlaiKi 



Peru 



New England . 

 California. ... 



Patagonia 



Japan 



("alifornia. . . . 



Key West 



(Taiapagos 



Tobago 



Tobago 



Tuamotu 



California 



Latitude. 



39° 35' N. 

 72° 48' N. 



(?) 



42° 45' N. 

 33° 58' N. 

 46° 47' S.. 



(?) 



33°35'M. 

 24° 25' N. 

 Equator. . 



11° 25' N. 

 11°25'N. 

 14° 24' S.. 

 24° 30' N. 



These figures, like those for the orinoids, seem to show a variation dependent upon tempera- 

 ture, at least so far as temperatures have been determined or can be inferred. The sea urchms 

 from cold regions are relatively low in magnesia; those from the Tropics are high. There are, 

 however, two apparent exceptions. The urchin from the coast of Peru probably owes its abnor- 

 mality to the cold Humboldt current, which flows northward from the Antarctic Ocean. Encope 

 micropora is also seemingly anomalous, and its high percentage of magnesia is difficult to ex- 

 plain. Unfortunately the actual temperature of its habitat is not given. 



Two publislicd analyses of sea urchins are worth reproducing. They are: 



1. Echinus (Stron(i!,lo,Tnlrot„s?) rkobwhimsis. North Sea: analysis by L, Schmelck. Noi-ske Nordhavs Exped,, 

 No. 28, p. 129, 1901. „ ^,. ^, ,, „ „., 



2. Echinus csailmlus. Locality not .-stated, pn.l.ablx Mcdilerranean: analysis by (). Butschli. k. (u-sell. Wi.ss. 



Gottingen Abh., No. 3, 1908. 



Oli/<r an(iliisi>! of std urcluns. 



Although different in minor details these analyses arc fairly comparable with ours. The 

 urchin analyzed by Schmelck was from the far north, and its composition is very near that of 

 our specimen from Greenland. Biitschli's sea urchin is doubtless from warmer water and shows 

 the liigher ligiu-e for magnesium carbonate. 



3. STABFISHES. 



In the former e.lition of tliis paper the starfishes and brittle stars were treated as one 

 series, and onlv eleven analyses of them were made. Now, when a much larger mass of ma- 

 terial is available, it is better to separate the two groups of organisms. Twenty-nme star- 

 fishes have been analyzed, of which two from Tobago were given us by Dr. Hubert L. Clark. 



