IQ2 SMITHSONIAN INSTITUTION 



blairi. Miller afterward discovered its resemblance to Mespilocrinus, but refused to admit 

 its identity because his specimen had five infrabasals. He happened to be short of names at 

 that moment and therefore spared us the infliction of another generic synonym. The pres- 

 ence of the genus has been distinctly recognized from fragments in the Kinderhook beds of 

 Fern Glen, Missouri, and it is represented by good specimens in the equivalent beds of 

 Indiana and Kentucky. 



De Koninck and Le Hon's species occurs in the lower limestone at Tournai, Belgium, 

 substantially equivalent to the horizon of the Lower Burlington, or Choteau beds, as devel- 

 oped in Iowa and Missouri. Phillips figured under the name "young Potefiocrinus" a 

 specimen from the English Mountain limestone which undoubtedly belongs to this genus, 

 and probably to the type species. Phillips was not blind to its peculiarities, and figured it to 

 show the arms in a rudimentary state. In America the genus does not occur later than the 

 Burlington limestone. 



Mespilocrinus is a very rare form, three of the species being represented by single 

 specimens. I have tried for years without success to obtain a specimen of the Belgian species, 

 only two having been found, to my knowledge, at Tournai since De Koninck's time ; and in 

 his large collection, acquired by Professor L. Agassiz for the Museum of Comparative 

 Zoology, the species is not represented. Of the most characteristic species we have better 

 material, but outside of the original Barris and Wachsmuth collections at Harvard, and my 

 own, very few specimens are known. 



The characters ordinarily available for the separation of species are not much differen- 

 tiated in this genus, and we have to rely to some extent upon its erratic development in some 

 of the broader characters, among which, however, I do not reckon that of the infrabasals, 

 which I regard as purely individual. 



The species may be arranged as follows : 



The Species of Mespilocrinus 

 I. Arms in close contact. 



Rays asymmetric with dextrorse twist. 



Specimens large, column regularly cylindrical. 



Short columnals with straight sides M. forbesianiis. 



Specimens small, sutures not indented. 

 Crown turbinate, with large column facet. 



Column large, composed of rounded columnals, changing 



from short proximally to very long and spindle-shaped M. konincki. 



Crown globose, . column facet small M. blairi. 



Sutures between Br beveled. IBr half as long as RR. IIBr 2 and 3. .M. romingeri. 

 Rays symmetric, without twist. 



Specimens large. Sutures not indented. 



Br very short and wide ; IBr not over one-fourth length of R. 



IIBr 6 or 7 M. bordeni. 



II. Arms not in close contact. 



Rays symmetric, without prominent twist. 



Specimens small ; crown ovoid, higher than wide ; IBr nearly as 



high as RR M. thiemei. 



Specimens large ; crown subglobose. 



IBr half as long as RR; columnars becoming elongate, but not 



spindle-shaped M. chapmani. 



