132 



SUPPLEMENT TO THE 



only differ from Amhoccelia umbonata by the presence of a longitudinal mesial groove 

 in both valves. Prof. Hall mentions the existence of five known American species of his 

 genus in the Devonian and Carboniferous Rocks of the United States. 



Whether Ambocoelia is generically separable from Spirifera proper must remain a 

 question for further consideration. The quadruple muscular impressions in the interior 

 of the dorsal valve represented in Prof. Hall's figure would certainly constitute a good 

 generic character, and I have never observed them so placed in any of the species of 

 Spiri/era that have come under my notice. 



We must now append to the Table of the distribution of spiral-bearing Brachiopode 

 in time we have given in p. 85 the following genera. 



Genera. 



•1 



1 



o 



c 

 .2 



a 

 1 



1 



1 



3 



1. famYy— Spirifeeid^, King, 1846. 

 AmboccElia, Hall, 1860 















2. Family — Nucleospirid^, Bav., 1881. 

 Hindella, Da»., 1882 









4. Family— kTVixviUM, Ball., 1877. 

 Anazyga, Bav., 1882 ... ... 





What has been stated in the Devonian and Silurian Supplements in connection 

 with the spiral-bearing genera and species has shown how absolutely necessary and 

 important it is to become acquainted with the position and direction of the spiral coils, 

 their attachments to the hinge-plate, and the shape of the lamellae or loop by which the 

 principal stems are connected, before we can assign to unworked forms their correct 

 generic position. 



In this last category, that of unworked forms, the following British species must be 

 placed, and their interior arrangements sought for : 



