Wiuchell. '*'^'* [MayG, 



6. Generic and sub-generic types of a carboniferous character. The 

 most important genera possessing a i^aleontological vahie in this discus- 

 sion are tlie following : 



Actinocrinus. Edmondia. 



Producta . Sanguinolites. 



Aviculo pecten. Cardiomorpha. 



Mytilus. Nautilus. 



Myalina. Phillipsia. 



The genus Actinocrinus begins its existence in the upper Silurian, but 

 attains only a feeble development until we reach the lower carboniferous. 

 It seems to reach its culmination in the Burlington Limestone. Accord- 

 ing to a table drawn up by Dr. B. F. Shumard'^^ in 1865, this genus is 

 represented by two species in the Niagara group, 2 in the Corniferous ; 6 

 in the Hamilton; 3 in the Chemung; 115 in the Burlington Limestone 5 

 29 in the Archimedes Limestone, and 2 in the Kaskaskia Limestone. Later 

 investigations render it necessary to change these figures without materi- 

 ally altering their ratios. It is emphatically a Carboniferous genus. Of 

 this genus seven or eight species are known in the Marshall group; and 

 they also belong to those peculiar types which characterize the Carbonif- 

 erous limestone (Compai*e for instance A. 'pistilUformis). 



The genus Producta, in its sub-generic forms, has a similar history. It 

 begins in the lower Devonian and culminates in the Lower Carboniferous. 

 Professor Hall describes 11 species from the Chemung group of New York. 

 I am acquainted with 20 species (including one Strop?ialosia?), from the 

 Marshal] group. De Koninck describes 28 sj^ecies from the carbonifer- 

 ous rocks of Belgium. D'Orbigny enumerates 63 known species of Pro- 

 dticta,^^^ of which one is Silurian, 4 are Devonian, and 49 are Carbonif- 

 erous. Bronn enumerates'^^ 45 species as certainly discrimhiated, of which 

 37 belong certainly to the Mountain Limestone, and only two occur in rocks 

 as old as the Devonian. 



Of the genus Spiriferina we have three species in the Marshall gi-ouj). 

 No species have ever been recognized in rocks as old as the Devonian. 



The genus Aviculopecten is emphatically a Carboniferous type, and 

 was so regarded by McCoy when first proposed. In his descriptions 

 of British Paleozoic Fossils, he enumerates 18 species of the genus, 15 of 

 which belong to the Carboniferous system, and 3 to the Old lied Sandstone. 

 Nine species are reported from the Carboniferous rocks of Illinois. From 

 the Marshall group I am acquainted with 12 species (including 4 species 

 of Pernopecten not heretofore separated from Aviculopecten). It is true 

 the Chemung contains also several species; but as the type is not known 

 to descend lower, the presence of these species in the Chemung unites 



'25 A catalogue of the Palaeozoic Fossils of North America I. Echinodermata. 

 126 Prodrome de Pal6ontologie. 

 12' Index Palseontologicus. 



