BRACHIOPODA. 133 



ridge. The mutual relations of the different parts of the internal apparatus 



Fig. IJO. Fig. 121. 



Figs. 120, 121. The brachidium of Anoptotkeca [Bifida) lepida. 

 Fig. 120. A lateral view, showing the relations of the loop to the median septum and ridge. 

 Fig. 121. A posterior view from behind. 



(c) 



are better seen in the accompanying constructive figures (120, 121), one 

 representing a view of the interior from the side, the other from the umbonal 

 region. 



This structure shows an admirable adaptation in the loop for resistance 

 to strains ; the slotted median ridge of the pedicle-valve is short and thick, 

 extending for about one-half the length of the shell, and is most deeply 

 excavated at the point where the stem of the loop is inserted. (See figure 

 of the interior of this valve given on Plate LII, fig. 19.) The cardinal 

 process in this species has not, so far as we are aware, been described or 

 figured, but our sections show that it is quite similar to that of Anoplotheca 

 venusta, as described by Sandberger and Soess. The latter species also has 

 the median septum in each valve, and though the character of its loop is 

 not known, it will be shown that in similar forms from American faunas this 

 organ possesses the same structure as in Terebratula lepida. It is highly 

 improbable that two species, so closely similar in external and internal 

 characters as Anoplotheca venusta and Bifida lepida, and coexisting in the same 

 fauna, are not congeneric. Therefore, with our present knowledge, it seems 

 necessary to conclude that the term Bifida is altogether synonymous with 



AlNOPLOTHECA. 



