366 NEW BRACHIOPOD FROM TRENTON LIMESTONE WALCOTT. 



the sides and front of the shell. With this structure the interior of the 

 shell would have five radiating ridges gradually widening out from the 

 apex and becomiug hollow towards their outer ends. The cast of the 

 interior of the shell, near the apex, shows that one of the ridges joined 

 a thickened portion of the shell that was probably the support of the 

 si phonal tube, as in the genus Acrotreta. 



1. Side view of the partial cast of the interior. Greatly enlarged. 



2. Summit view of fig. 1, to show the character of the cast of the interior surface exposed. The 



' " 3. Front view of another specimen that shows the cast of the ridges on the interior of the shell, 

 and the thickened apex. . . 



4. A more, acutely conical shell, associated with the preceding. 



The conical form varies considerably. One of the specimens is rela- 

 tively one-third broader at the base than the other that otherwise is 

 identical with it. 



Two of the specimens are in the U. S. National Museum collections ; 

 the third is from the Museum of Comparative Zoology, Cambridge, 

 Massachusetts. 



, The specific name is given in recognition of the long-continued services 

 of Mr. William P. Rust, in collecting the Trenton fauna of central New 

 York. 



Nat, Mus. Cat, No. 18443. 



