12 LARVIFORM CRIXOIDS 



our tiny American species, the question arises — can these forms he referred 

 to the family Allagecrinidae ? The American species in structure and ap- 

 pearance closely resemble the pentamerously symmetrical examples described 

 from Timor. These in turn cannot, according to Warmer's opinion, he 

 separated generically ■ f rom multi-brachiate forms. Finally the dorsal cup 

 of A. jakovlevi, the most abundant many-armed East Indian species, closely 

 resemhles the less known A. austiiiii (restricted). It would appear therefore 

 to he most convenient, conservative, and probably correct to consider all of 

 these crinoids as members of a single family and consequently the new genus 

 KalUmorphocrinns is assigned to the family Allagecrinidae. 



Wanner has been influenced by his observations on that peculiar series of 

 crinoids which he included in the family Hypocrinidae, to conclude that the 

 Timoran species referred to Allagecrinus are also the result of regressive evo- 

 lution and were descended from more complicated forms [17, p. 13]. Also 

 it is his opinion that the pentamorouslv symmetrical forms were derived, by 

 a reduction in the number of arms, from those possessing axillary radials 

 and as substantiating evidence he points out that in the highest Paleozoic beds 

 of Timor the five-armed species greatly predominate. 



This argument loses its significance in view of the numerous American 

 lower Pennsylvanian species which are not accompanied by any forms pos- 

 sessing axillary radials. Moreover a proper understanding of the so-called 

 Allagecrinus onicriraiuis Rowley from the lowermost Mississippian reveals a 

 primitive type of calyx from which the later forms may have been derived 

 by progressive evolution. It appears therefore that Kallimorphocrinus, ex- 

 cept for its specialized articular facets and the absence of an anal plate, is 

 in other respects truly a primitive crinoid and was not derived by degenera- 

 tion from a more highly specialized ancestral type. 



In view of its possible bearing on the ancestry of KaMmorphocrinus, 

 Allagecrinus amcricaiiits Rowley, which represents a more primitive hut allied 

 type, is here described. Because its peculiarities sharply differentiate it from 

 all other known crinoids, the new. genus Hybochilocrinus is introduced for 

 its reception. This genus is also assigned to the Allagecrinidae. 



Genus HYBOCHILOCRINUS" J. M. Weller, n. gen. 

 Genotype Allagecrinus americanus Rowley 

 Monocyclic larviform crinoids which are composed of three rings of 

 plates as follows: (1) a basal disc the plates of which are rarely distinguish- 

 able — some specimens seem to indicate that the basals are three in number 

 one being somewhat larger than the others, but the orientation of this larger 

 plate is uncertain; (2) five nearly equally sized radials; (3) five orals, the 



' vpos, humped; xeiXos, edge. 



