UINTACRINUS: ITS STRUCTURE AND RELATIONS. . 1" 



A young individual on the same slab, having arms preserved to abo\it 

 30 cm., gives the following measurements : — 



At 10th IIBr . . . length 1.00 mm. . . . width 2.25 mm. 

 " 18 cm. ... " l.on " ... " 1.75 " 

 " .30 " ..." 1.00 " ... " 1.50 " 



Allowing the same taper observed above for the terminal part of the 

 arm, the arms of this specimen would be about 55 cm. long. 



It will be observed that in the above measurements the distal brachials 

 are about as long as wide, while the proximal, or those nearest the calyx, 

 are five times as wide as long in the adult specimen, but only about twice as 

 wide as lono; in the young. The absolute length of the brachials does not 

 materially change, but remains nearly the same throughout the arm until 

 near the distal end, where they shorten rather rapidly ; but the ratio of 

 width to length changes very greatly, especially in the adult individual. 

 Near the calyx the brachials of VIII a are five times as wide as long, 

 whereas near the distal end of the several specimens examined the length 

 and width of the brachials are about equal. 



The two specimens, VIII a and h, representing the adult and young 

 forms, are shown on Plate I., just as they lie upon the slab, except that they 

 are reduced to about one-fourth natural size. The plate was taken from a 

 carefully executed drawing about half natural size, made by Mrs. Ricker, 

 reduced by photography to its present dimensions. The slab contained 

 numerous other specimens which were not drawn, except one or two 

 which interfered with portions of the arms of VIII a. 



There is a very extensive development of .syzygies in the.se specimens. 

 The}' occur throughout the arms in profusion, and there is a marked 

 uniformity in their distribution in the proximal parts of the arms in adult 

 specimens at intervals of 3 to 6 ; but farther up the intervals become much 

 more irregular, and often longer. I give below tables of the occurrence of 

 syzygies in several specimens from Locality No. 3, in which they are very 

 plain, and also some from Locality No. 1, including one long arm of speci- 

 men I XX, to a length of 24 inche.s. In counting, I reckon the syzyginl 

 pair as two brachials ; thus in the tables, the numbers given are those of 

 the hypozygals. In some places, indicated by dashes or other signs, the 

 positions of the syzygies could not be ascertained ; otherwise the succession 

 of numbers shows the actual intervals. The size of the specimens is indi- 

 cated by the width of the calyx in millimeters. 



