60 



Assuming that the above are all the described species of this series of 

 rocks, the fauna of the Potsdam as at present known would appear to con- 

 sist of 



Plantae, 6 species. 



Protozoa, 2 



Graptolitidse, 1 



Brachiopoda, 21 



Gasteropoda, 5 



Annelida, 5 



Crustacea, 67 



107 



The six species of Plantae are supposed to be fossil sea-weeds, and there 

 can be no doubt that at least four of them are ; but as to the two species of 

 Scolithus there is much difference of opinion. By some they are thought 

 to be casts of annelide-burrows, and by others fucoids. Much further of 

 observation is required to determine the affinities of these obscure but very 

 remarkable fossils, The two species of Archeocyathus may possibly belong 

 to an extinct order of corals, but for the present they are placed among 

 the Protozoa. The Graptolitidae, Brachiopoda, Gasteropoda, and Anne- 

 lida are mostly of genera or sub-genera, which have a great vertical 

 range, and can scarcely be made available to determine, by their generic 

 relations, the age of any geological horizon, although certain species of 

 each genus may be confined to, and characteristic of, particular groups of 

 strata. In the following comparisons, therefore, they will not be taken 

 into account further than to notice that none of the species are as yet 

 known to ascend into the Calciferous formation. The trilobites belong to 

 the following genera : 



Aglaspis, 1 species. 



Arionellus 4 



Bathy urus 4 



Bathynotus 1 



Chariocephalus 1 



Conoc^phalites 23 



Crepicephalus 2 



Bikelocepbalus 10 



Menocephalus 1 



Lonchocephalus 2 " 



Olenellus 2 " 



Ptychaspis 1 " 



Triartbrella 1 " 



The above constitute the dominant family of the trilobitic 

 fauna of the Potsdam. 



Agnostus 4 " 



Amphion 1 " 



Illaenurus 1 " 



Pemphigaspis 1 " 



Protichnites 6 " 



Climactichnites .... 1 " 



67 



