NO. 1S50. KXOB^^TOXE CRTXOID PAVyA—f^PRIXOER. 181 



part of it. While there is some difference in species between this 

 and the beds called Lower Burlington, yet the general type remains 

 the same, and there is no such extinction of genera and of con- 

 spicuous species as is found between the later members of the for- 

 mation. Below this bed are a number of irregular layers, mostly of 

 limestone, some of them oolitic, brecciated, or shaly, and some of 

 sandstone; all of them extremely variable locally and in many places 

 absent; but everywhere at the base of the formation is a great thick- 

 ness of argillaceous and sandy shales overlying the Black Slate. If 

 the crinoidal content of the formations is to govern, it would prob- 

 ably be more logical and would simplify the geology of the forma- 

 tion if all these beds above the heavy shales and lower sandstones 

 were ranked with the Lower Burlington as one member. Those 

 parts of the formation embraced in the Upper Burlington and 

 Keokuk, representing a period of culmination and extinction, are 

 of relatively restricted extent, wliile the earlier portion, namely, 

 Lower Burlington -Choteau-Waverly-Kinderhook (in part), is of 

 very wide geographical distribution. It is found on the flank of 

 the Rocky Mountains, in New Mexico and Montana, and the Moun- 

 tam Lunestone of Great Britain and Belgium is substantially its 

 equivalent, containing most of its characteristic genera, and many 

 species scarcely distinguishable, but none of those peculiar to the 

 succeeding members here. 



No one acquainted with the fauna of tliis formation, as disclosed 

 at numerous localities in the typical region above indicated, would 

 ever mistake a set of crinoids from the Lower Burlington for Keokuk, 

 or the opposite. Wliile a few of the more generalized forms, like 

 Oyathocrinus, are similar, the characteristic species are widely 

 different, and several important genera have become wholly extinct 

 witliin the Burlington, e. g., Megistocrinus, Amphoracrinus, Cacto- 

 crinus, Steganocrinus, Teleiocrinus, Strotocrinus, the discoid Platy- 

 crini, MeticJitJiyocrinus, Mespilocrinus, Wachsmuthicrinus, Belemno- 

 crinus, and the blastoid genera Orophocrinus, Scliizoblastus, Crypto- 

 hlastus, Orbitremites, and Codaster. On the other hand, the paired 

 arm structure so frec[uent in the Keokuk — as in Dizygocrinus — is 

 known in but one species in the Lower Burlington; the large and 

 rugose Actinocrini, Dorycrini, and Agaricocrini are represented only 

 by a few small and delicate species ; and the important genera of the 

 Flexiblia, Onychocrinus and the so-called Forhesiocrinus of the type 

 of F. woriheni, etc., not at all. In the typical region there is no 

 trouble whatever in distinguishing these beds by their crinoidal 

 fauna. 



But when we come to species described from the southern Indiana- 

 Kentucky-Tennessee region, and the collections made therein by Lyon, 

 Safford, Wachsmuth, Greene, and others, I have been constantly 



