200 rROCEEDINQS OP THE ACADEMY OP [1886. 



in form and size. The two lateral rays are composed of a large 

 radial, which is followed b}'^ two ver}' small brachials. The an- 

 terior ray has two radials, which combined are smaller than the 

 single lateral ones. The two are generally separated by the lateral 

 radials Avhich join between them, placing one of the plates at the 

 upper, the other at the lower end of the calyx. This peculiar 

 structure has evidently' prevented all former writers from recog- 

 nizing those plates as radials. That the}'- are radials, and were 

 gradually separated in the course of palseontological times, is 

 proved by Hall's Silurian species Calceocrinus chrysalis and 

 Galceocrinus ineequalis Billings,^ by C radiculus Ringueberg and 

 G. Barrandii Walcott, in all of which the plates are narrowly 

 elongate, and united by a short suture. In Galceocrinus goth- 

 landicus of Upper Silurian age, they are separated, but the first 

 radial extends almost to the second. In Calceocrinus clarus and 

 Galceocrinus Barrisi from the Devonian, the distance that sepa- 

 rates them is somewhat greater ; while in all Subcarboniferous 

 species the two plates stand widely apart. 



Galceocrinus agrees with Gatillocrinus in the arrangement 

 and form of its plates. In both of them the second ring consists 

 of five extremely irregular pieces, but, while in the latter all five 

 are arm-bearing, those of Galceocrinus are arm-bearing only in 

 the three anterior rays. The two posterior ones are small and sup- 

 port a large tube. The corresponding plates in Gatillocrinus 

 support upon one end of their upper side an arm, upon the other 

 a similar tube as Galceocrinus, and in both genera the two antero- 

 lateral rays are far stronger developed than any of the others. 

 The two forms resemble each other more closely than might be 

 expected from Crinoids that ditfer so widely in their general 

 aspect, as shown by changing Gatillocrinus from its natural posi- 

 tion into that of a Galceocrinus. This may be done theoretically 

 by pressing the calyx sideways in such a manner that the basals 

 are pushed over to one side, and the three arm-bearing radials to 

 the opposite side. The lateral ones, however, owing to their large 

 size naturally extend to the basal side, where they join the small 

 postero-lateral radials, which, as stated, hold a similar position 



* It was Mr. Walter R. Billings, of Ottawa, who already in 1883 directed 

 our attention to Heierocrinus inmqualis as being a Calceocrinus, and he 

 informed us also that in this species the two anterior radials were joined by 

 sutures. 



I 



