Bivalve Shells of Nova Scotia. 123 



Journal of Geological Society, Vol. X, 1853 ; Supplement to Acadian 

 Geology, 1860, p. 43; Salter, Journal of Geological Society 

 (Anthracoptera), Vol. XIX, 1863, p. 79 ; Acadian Geology, 2nd 

 Edition. 1868, p. 204 ; Wheelton Hind, Journal of Geological 

 Society, VoL L, 1894. 



This is the most common species of the genus, and is very 

 abundant in some shales and bituminous limestones of the 

 coal-formation. So much is this the case, that some thin 

 beds may be said to be made up of these shells, which 

 though somewhat strong, are often much compressed and 

 distorted, so that it is often very difficult to obtain perfect 

 examples. In 'beds where they are less plentiful they are 

 usually much flattened, by which the general outline of the 

 shell is greatly modified. Owing to these circumstances 

 and also to the fact that the shell is rounder when young 

 and becomes more angular and elongated with age, it is 

 difficult to select typical specimens, and hence the pub- 

 lished figures are very dissimilar, (compare the figures in 

 my paper of 1853 in "Acadian Geology" second edition, in 

 Salter's paper of 1863, and in Wheelton Hind's paper of 

 1894, or figures 1, 2 and 3 of this paper). 



This shell is very near in form to Naiadites modiolaris 

 (Avicula modiolaris of Sower by), and also to some forms of 

 N. tumida Etheridge, resembling them in some respects so 

 closely that it is difficult to distinguish some of the Nova 

 Scotian specimens from these English forms. It is also 

 near to N, {Modiola) Wyoming ensis Lea, of the Pennsylvania 

 coal measures. These forms may certainly be regarded as 

 representative species. 



It is not improbable that some of the shells from the 

 Carboniferous of Illinois and Ohio, which have been referred 

 to the genus Myalina, belong to this genus, as suggested by 

 Dr. Hind. Meek and Worth en have also referred a species 

 from the Keokuk group (Lower Carboniferous) to the genus 

 Anthracoptera (Naiadites) — A. fragilis M.. and W. 1 White 

 has described N. Polita {Anthracoptera politd) from the 

 coal measures of the West. 2 



1 Chicago Academy, 1880. 



2 U. S. Geological Survey, XII, 1880, p. 166. 



