of Burlington^ Iowa, and its Vicinity. 223 



The Lamellibranchiata, with but few exceptions, have 

 not been observed above the base of No. 7. One of these 

 is a Pecten in No. 8, another a Pecten in the lower portion 

 of No. 7, and another is the Avicu/a circulus of Shumard, 

 which is also found in the lower portion of No. 7. In 

 some of the lower beds, the Lamellibranchiata are almost 

 as numerous as the Brachiopoda. 



The Crinoida are the prevailing forms in the upper 

 beds, which present, in this respect, a striking contrast to 

 the lower beds. Portions of crinoidal stems have been 

 found in all the lower beds, but no parts of their bodies 

 have been observed below No. 6. In this bed, the genera 

 Platycrinus, Rhodocrinus, and Actinocrinus have been 

 recognized by the discovery of fragments of their bodies. 

 In the lower portion of No. 7 the same genera have 

 been recognized, with the addition of Poteriocrinus, Homo- 

 crinus, and Pentremites. Their remains are far more 

 abundant here than in the beds below, but less so than in 

 the upper beds. Of other Echinodermata, at least two 

 species of Archiocidaris have been discovered ; one in the 

 lower and middle portions of No. 7, and another in No. 8. 

 A species of Sjnitang-us ? has also been recognized in the 

 middle portion of No. 7. 



By taking the foregoing view of the proper separation 

 of the fossils of these rocks, it will be found that the num- 

 ber of species of the Brachiopoda formerly considered as 

 Carboniferous is considerably reduced. From present 

 indications, it is thought that there are but some ten or 

 twelve true Carboniferous species of this order in the 

 upper beds, the greater portion of which are published by 

 Prof. Hall in the Iowa Reports. 



The peculiarities of these, as compared with those of 

 the lower beds, are easily recognized. The genera are of 

 larger size, respectively, and the Spirifers, in particular, 

 are of more compact and rounded forms, and are destitute 



