BRACHIOPODA. 
145 
angle with the lateral branches of the loop, and is deflected posteriorly; its 
surface is generally cylindrical, but in Nucleospira concentrica it is considerably 
flattened. 
Fig. 130. Fig. 131. 
Fig. 123. A preparation of Nucleospira ventricosa, Hall; showing the umhonal blades, the loop and the form of the 
first volution of the spirals. 
Figs. 129, 130. The primary lamellas and loop of Nucleospira ventricosa, Hall. 
Fig. 131. A preparation of JlfMcZeospira conciJina, Hall; showing one-half of the brachidium, the mode of attach¬ 
ment of the crura to the umhonal 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. concentrica and N. rotundata, Whitfleld, 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 
