DISCOVERY OF THE DISK OF ONYCHOCRINUS 515 



from those given by Wachsmuth and Springer in the Revision oj the 

 Palaeocrinidae, Part I. Discovery and research since that time have 

 greatly added to our information touching this group, which was then 

 by no means well understood. In Gnorimocrinus the typical species 

 is G. expansus Ang.,'^ and several of the species listed under this 

 genus in the Revision are now found to belong to other genera. 

 For instance, G. excavatus Schultze doubtless belongs to Dactylo- 

 crinus; and perhaps G. ohlongatus and G. rigens also. G. ovalis, 

 saJteri, interbrachiatus, and austini I* have referred to a new genus, 

 Protaxocrinus; while G. loveni, by reason of its possession of three 

 primibrachs, and a radianal in addition under the right posterior 

 ray, will form the type of another new genus, for which I propose 

 the name Meristocrinus. 



In Lithocrinus the typical species is L. divaricatus Ang. (including 

 L. rohustus syn),^ which has no radianal; while for L. ohesus, which 

 has a radianal, and apparently a different interbrachial structure, 

 I have found it necessary to propose a new genus, Cholocrinus. 



Under Onychocrinus there are two well-marked types, represented 

 by O. ramulosus and O. exsculptus, which probably might be separated 

 generically. The first has three primibrachs, and the latter four; 

 and besides this, the habitus of the two species is so distinct that they 

 can be recognized from the smallest fragments. The exsculptus 

 type runs from the Burlington to the St. Louis, and probably to the 

 Kaskaskia, and the ramulosus type from the Keokuk to the Kaskaskia. 



In like manner, I think it probable that Forbesiocrinus agassizi 

 with its two primibrachs, should be separated from the other species 

 of the genus, which all have three. In fact, the analysis of the genera 

 indicates the definition of other new genera which will have to be 

 proposed, in order to cover cases already known or hereafter to be 

 discovered. 



The analysis of the Flexibilia genera here given is an improvement 

 upon the former one, resulting from the foregoing observations. In 

 considering any such arrangement, reasonable latitude must be 

 allowed in construing descriptive terms, which cannot be made to 

 fit all cases by any hard and fast lines. It must not be forgotten 



I Iconographia Crinoideoruni, Plate XX, Figs, i^, 16. 

 ^Ihid., Plate XXI, Figs. 11, 12, 21. 



