UINTACEINUS: ITS STKUCTURE AJND RELATIONS. 



65 



the specimens being more or less flattened by pressure, we can only give 

 the relative size of the calyx by taking its width in its present con- 

 dition ; the diameter of the calyx in life may be taken as approximately 

 60 per cent of the width thus given. 



These measurements show that in their arm structure the specimens 

 from Locality No. 2, and the small ones from Locality No. 1 as well, 

 exhibit most decidedly the characters of the young individuals. While, 

 as in the different parts of the arm of the young Antedon, the absolute 

 length of the brachials does not differ so very much in the different 

 specimens, the increase in width is very marked as the size of the 

 specimens increases. In the smallest specimens from Locality No. 2 the 

 length of the brachial is about equal to its width. Taking the average, 

 it appears that in specimens 25 mm. wide or less, the width is less than 

 twice the length ; in those from 25 to 37 mm. it is about three times ; 

 in these from 37 to 50 mm., about four times; while in those of maxi- 

 mum size — 50 mm. and over — the brachial is about five times as wide 

 as long. 



From the smallest to the largest specimens the brachials increase in 

 length only from .50 mm. to 1.75 mm., while in width they increase from 

 .75 mm. to 8 ram. We have thus a progressive increase in width of the 

 arm which is remarkable for its uniformity in relation to the size of the 

 calyx. Such increase is substantially parallel to that which takes place 

 from the young to the adult Antedon. It must be remembered that the 

 young Antedons measured by W. B. Carpenter were in the pentacrinoid 

 stage, much yoimger, relatively, than our specimens, and therefore the 

 width of the arm-segments was proportionally less. But the increase in 



