ACEOCRINID^ W. and Sp. (1885). 



Monocyclic. Basals separated prom the radials by a large belt of accessory 

 PIECES. Radials in contact except at the posterior side, where they are 

 separated by an anal plate. Structure otherwise as in the Hexacrinid^. 



Geological and Geographical Distribution. 

 Number of known species. 



FOKJIATION. 



ACEOCETSUS. 



Carboniferous. 



Coal Measures. 



1 



Suboarbonif erous . 



Kaskaskia group. 



1 



St. Louis group. 



1 



Total species 



3 



Remarks. — This family consists of the single genus Acrocrinus, which is 

 only known from America, where three species have been found : one in 

 each of the upper members of the Subcarboniferous, and one in the Coal 

 Measures. It represents, therefore, the end of the Camerata, so far as our 

 present knowlege goes. It appeared after all the other families were extinct, 

 except a small remnant of the Platycrinidse represented by a small but very 

 prevalent species, and the Hexacrinidce, from which its derivation is very 

 apparent. It survived in the Carboniferous, from which a single very small 

 specimen is knqwn. 



In the interposition of accessory pieces between the primary plates of the 

 calyx, the Acrocrinidse approach the Reteocrinidse ; but the two families 



