13 



as stated, in Ohio Pal., vol. 2, p. 163, an arm formula of 4+3 + 

 2+3+4—16 arms, or 4+3+2+4+4=17 arms. We are inclined to 

 think that two species are described here under one name; but speci- 

 mens from that locality are very poor, and those which we have, 

 possess only sixteen arms, and we cannot throw any additional light 

 upon the subject. The reference of the species, however, to Agajri- 

 eocrinus is very doubtful. 



Agaricocrinus nodulosus from the Keokuk Group has 17 arms. 

 The arm formula is 4+4+2+4+3. And A. macadamsi has IS 

 arms. The arm formula is 4+4+4+3+3. This species is one of 

 the largest, has the most numerous arms and belongs to the last of 

 the race. 



We have thus taken, briefly in review, all the species of AgaxifiQ- 

 crinus that have been described. They belong to the Chouteau. 

 Burlington and Keokuk Groups. Names have been given to forty 

 two species. All of these have been illustrated excerjt five, three of 

 which are believed to be good and valid species and the other two 

 may be classed as doubtful, because they were named thirty six years 

 ago and have never been illustrated, and some authors have said they 

 are synonyms. All we can say is that we have not identified them in 

 our collections. It is very easy for some to say, that one species is a 

 synonym for another, but the student will find that good authors 

 rarely make a synonym, and, if one occurs, it is under such cir- 

 cumstances that ordinary prudence will not guard against it. We 

 have seen ten-armed species described by Hall, from the Burlington 

 Group, twelved-armed species described by Hall from the Burling- 

 ton Group, twelve-armed species described by Meek & Worth en from 

 the Burlington Group, and twelve-armed species described by Hall 

 from the Keokuk Group, all of which have been finely illustrated, and 

 occur, in Iowa and Illinois, classed as synonyms for Agaricocrinus 

 americanus, which has never been described, but which isafourteen- 

 armed species, as shown by the illustrations, and has never been 

 known to occur, except in the Keokuk Group of Tennessee. Such 

 erroneous classifications are without any discrimination; and usually 

 without examination, but there is no way of preventing the preten- 

 sions. 



We would again call attention to the distribution of the species in 

 the different Groups of rocks. The species from the Chouteau lime- 

 stone are small and bear either nine or ten arms. Those from the 

 Burlington Group are larger than those from the Chouteau, but are 



