I.ARVIFORM CRINOIDS 13 



posterior one being somewhat larger than the others, its inner angle extend- 

 ing between the anterior orals for a short distance thus completely separating 

 the two postero-lateral orals from each other. In addition to these three 

 rings of plates a single small anal plate rests upon the beveled upper left- 

 hand corner of the right posterior radial and extends upward above the 

 upper surfaces of the radials. The radials were all arm-bearing and in most 

 specimens only a single arm was present upon any one radial. A few rather 

 poorly preserved individuals may possess radials which are axillary but this 

 can not be stated as a certainty. 



The single species for which this genus is erected is similar in a general 

 way to the forms of Kallimorphocrinus described on subsequent pages. It 

 is however a more primitive type as shown by the presence of an anal plate 

 which has been completely lost in the Pennsylvanian genus, and by the less 

 highly specialized arm facets. It is possible that these forms represent a 

 stage in the evolutionary history of Kallimorphocrinus. 



Hybochilocrinus americanus (.Rowley) 

 Plate I, figs, la-c 

 1895 Allagccrinus americanus Rowley, Am. Geol. vol. 16, p. 219, figs. 3-10. 



Louisiana limestone ; Louisiana, Missouri. 

 1908 Allagecrinus americanus Rowley, Missouri Bur. Geol. ser. 2, vol. 8, p. 67, pi. 16, 

 figs. 39-41. 

 Louisiana limestone ; Louisiana, Missouri. 



The only previously known American crinoid which bears even remote 

 resemblance to the Coal Measures species of Kallimorphocrinus is Allagc- 

 crinus americanus Rowley from the Kinderhook beds of Pike County, 



Fig. i 

 Plan of the calyx of Hybochilocrinus americanus 



Missouri. For the sake of comparison with the Coal Measures species a 

 description of this interesting Lower Carboniferous form is here included. 

 The material available for study consists of about one hundred specimens 

 collected from the type locality in 1896 by Professor Stuart Weller. 



