7G 



vault. And twenty-three species of Darycrinus, having ten, eleven, 

 twelve, thirteen, fourteen, fifteen, sixteen, seventeen, nineteen and 

 twenty arms, the prevailing species having twelve and sixteen 

 arms. 



There is no genus confined to the Keokuk Group, and all that 

 are found within it passed up from the Burlington Group below, 

 except Alloprosallocrinus. There are twelve species of Aciinocrinus, 

 having twenty-five, twenty-nine, thirty, thirty-eight and forty arms 

 or more. A peculiarity, in some of the species, as in Aciinocrinus 

 gibsoni, is the bifurcation of the arms after they become free, as 

 they do, in some species of Saccocrinus. The prevailing species 

 have thirty ambulacral openings to the vault. There are seventy- 

 two species of Baiocrinus, having twelve, fourteen, fifteen, sixteen, 

 seventeen, eighteen, twenty, twenty-one, twenty-two, twenty-four, 

 twenty five, twenty-six, twenty-eight, twenty- nine, thirty, thirty- two, 

 thirty-six and forty arms. The prevailing species have sixteen, seven- 

 teen, eighteen and twenty arms. There are eighteen species of Agari- 

 cocrinus, having ten, twelve, thirteen, fourteen, sixteen and eighteen 

 arms. The prevailing species have ten and twelve arms. There 

 is only a single species of Alloprosallocrinus, and it has eleven 

 arms. There is only a single species of Amphoracrinus. It was 

 originally referred to the Waverly Group and described under the 

 name of Aciinocrinus viminalis. It has only ien ambulacral open- 

 ings to the vault, but the arms bifurcate so that there are forty 

 arms in the superior part. The association of crinoids at Rich- 

 field, in Summit county, Ohio, very clearly indicates that the 

 rocks are above the Waverly Group and belong to the Keokuk. 

 There are seven species of Dorycrinus, having sixteen, seventeen 

 and twenty arms. The prevailing species have twenty arms. 



Authors have not clearly distinguished between the Warsaw and 

 St. Louis Groups, though most of the species are referred to the 

 Warsaw Group, and there are so few species we will consider the 

 two Groups together. First, it will be noticed, that no Aciino- 

 crinus are found above the Keokuk Group. Sixteen species of 

 Baiocrinus have been described, having seventeen, eighteen, 

 twenty and forty arms. The principal species have eighteen and 

 twenty arms. One Dorycrinus has been described having ten 

 arms and three species of Alloprosallocrinus. And here the 

 family of the Aciinocrinidce became extinct, unless Baiocrinus 

 copiosus is a representative of the Kaskaskia Group. It was 



