58 



Ernst Merker, 



V. 



n £D21 o = 1,47877 



'^Qpt Achse 



Licht 



Fig. F. 



n. caicit =1,48640 

 n £ Echin. =1,47877 

 Differenz = 0,00763 



C^ücht 

 Opt. Achse 



Fig. G. 



Leiocidaris] Stachel quergeschliffen. 



a £ = 51° 59' 



VI. 



N D21 o = 1,87747 



t = 21° 



Lichteinfall 



log sin a £ = 9,89643 — 10 

 log N == 0,27357 



log n £ = 0,17000 



n £ Calcit 

 n £ Echin. 



= 1,48640 

 = 1,47911 



n fiD21 o = 1,47911 



Differenz = 0,00729 



Asterias glacialis, Marginalplatte, senkrecht zur 



optischen Achse. 

 a £ = 51° 57' N D 21 o — 1,87747 

 log sin a £ = 9,89624 — 10 



VII. 



log N = 0,27357 





] gn £ =0,16981 





n eD21 a= 1,47847 





21< 



n £ caicit =1,48640 



l e Echin. 



= 1,47847 



Differenz = 0,00793 



Metacrinus acutus, Stielglied senkrecht zur Achse. 



t 

 -10 



a £ = 51°58' 



N D 20|5 o = l,87747 



20,5° 



log sin a £ = 9,89633 

 log N = 0,27357 

 log n £ = 0,16990 



