LARVIFORM CRINOIDS 29 



which slopes gently upward to the orals. The lateral surfaces of the ad- 

 joining radials meet to form a nearly plane surface in the middle of which 

 is the interradial suture. 



Xo structures for the support of arms are developed on any of the 

 radials nor is an anal opening visihle in the calyx. 



The oral dome, formed of five nearly equal plates which alternate with 

 the radials, constitutes a little more than a quarter of the total height of the 

 calyx and overhangs the radials so that when viewed from above none of 

 the lower plates are visible. The relation of the orals at the center of the 

 distal surface is not entirely clear but it appears that the two anterior plates 

 extend beyond the left and right posterior orals and fit into a notch in the 

 end of the posterior plate in the manner characteristic of Diclwstreblooimis 

 scrobiculus. They slope gently outward and downward from the center and 

 then turn sharply downward to meet the upper edges of the radials. The 

 upper surfaces of the orals have shallow depressions similar to those developed 

 on the oral plates of Kallirnorphocriniis. 



The surfaces of the plates are minutely irregular and porous. 



Remarks. — The systematic disposition of this little crinoid is a rather 

 perplexing problem. It is strikingly similar in form and appearance to certain 

 examples of Kallimorpkocrinus and differs from this genus only in the ab- 

 sence of arms and in the apparent relation of the orals at the center of the 

 distal surface which resembles Dichostreblocrinus rather than Kallimorpho- 

 cri nits. A. cdiosus can not be considered an immature stage in the develop- 

 ment of Kallimorphocrinus however as we have six similar specimens and 

 no intermediate stages. 



On the other hand A. odiosits is very similar to certain specimens con- 

 sidered to be immature stages of Dichostreblocrinus scrobiculus (p. 37). 

 From these however it differs in its more slender proportions and in the 

 character of the distal surface of the orals. 



Were it not for the character of its oral crown A. odiosus might be 

 referred to the Hypocrinidae. In this case the intermediate ring of plates 

 would have to be considered basals and the calyx structure would differ from 

 Acariaiocrinus only in the absence of a lateral anal opening. 



Occurrence. — These silicified specimens were obtained from a limestone 

 low in the Pennsylvanian section of Warren County, Indiana, near the center 

 of the X. j4 sec.35, T. 21 X., R. 9 W. 



FAMILY HYPOCRIXIDAE 



The family Hypocrinidae was erected by Wanner in 1916 who assigned 

 to it Hypocrinus Beyrich, Sycocrinus Austin, Cydonocrinus Bather and the 

 new genera Monobrachiocrinus, Thetidocrinus and Bolbocrinus [14, p. 88]. 



