BRACHIOPODA. 



146 



angle with the lateral branches of the loop, and is deflected posteriorly ; its 

 surface is generally cylindrical, but in Nucleospira concenirica it is considerably 

 flattened. 



Fig. 128. 



Fig. 129. 



FIO. ISO. Fig. 131. 



Kg. 188. A preparation of NueUtapira ventricota, Hall; ihowing the ambonal blades, the loop and the form of the 

 first Tolatlon of the spirals. 



Figs. 129, 130. The primary lamellae and loop of IfueUotpira ventrioota. Hall. 



Fig. 131. A preparation of NucUotpira concinna, Hall; showing onehall of the brachidium, the mode of attach- 

 ment of the erurs to the ambonal blades and the fiattened stem of the loop. (c.) 



The structure of the hinge-plate and brachial apparatus is now known in 

 the following species of this genus : N. pisum, Sowerby, of the Wenlock lime- 

 stone; N. pisiformis, Hall, of the Clinton and Niagara group; N. ventricosa, 

 Hall ; N. elegans, Hall, of the Lower Helderberg, and N. concinna, Hall, of the 

 Corniferous and Hamilton groups. Besides these, the following American 

 species have been described: N. concenirica and N. rotundata, Whitfield, of the 

 Lower Helderberg group, and N. Barrisi, White, of the Kinderhook. 



A single individual of what appeared, from external characters, to be the 

 species Nucleospira concinna. Hall, from the Corniferous limestone of the Falls of 

 the Ohio, affords a surprising variation in the structure of the loop. The 

 internal parts have the same development and mutual relations as in specimens 

 of the species from the Hamilton shales, except that the stem makes a slightly 



