Contributions to Palaeontology. 



99 



The fauna of this sandstone, other than that of the 

 crustaceans, is comparatively meagre, consisting of a few 

 species of Lingula, a Discina, an Obolella?, an Orthis, 

 two Gasteropods, one Theca and a Serpulites ? 



Of the lower orders of animal life, we have very little 

 at our disposal for its illustration. We know, however, 

 that the family of Graptolithle appeared in beds which 

 are somewhat above the centre of the formation. Crinoi- 

 dal columns are cited by Dr. Owen as occuriug in several 

 localities, and I have seen a single obscure specimen which 

 is apparently referable to this family of fossils. 



The absence of animal life, in greater variety of forms, 

 seems to be due to the unfavorable character of the sedi- 

 ment, rather than to any other cause. From the fact that 

 every bed, however thin, where there is an admixture of 

 sand with argillaceous matter, or with a small portion of 

 calcareous matter, is seized upon, as it were, for the habita- 

 tions of these animals, it is evident that it needed only a 

 more favorable condition of the ocean bed to have deve- 

 loped an extensive fauna. W"e are, I think, moreover 

 warrented in concluding that at some not far distant but 

 now unknown point, this condition did exist in a much 

 higher degree than in the localities investigated. 



In order to make this notice as complete as possible with the 

 materials I now possess, I have, with few exceptions, given illustra- 

 tions of the species known to me as occuring in this sandstone in 

 the Upper Mississippi valley. 



GR APT OLITID^E . 

 GENUS DENDROGRAPTUS (Hall). 

 DENDROGRAPTUS HALLIANUS (Prout). 

 Graptolithus hallianus : Prout, Am. Jour. Science (2), xi, p. 187, 1851. 



Frond proceeding from t a distinct root. Stems strong, 

 numerously branched : branches divaricating, and fre- 



