GENERA EHYNCHONELLA, LEIORHYNCHUS, ETC. 273 



Some of the species are only plicated towards the front, and the mesial 

 fold and sinus are often limited to the lower half of the shell. Even the 

 more distinctly plicated forms are comparatively broader and smoother 

 than any of the Rhynchonellce. When occurring in the same beds with 

 Rhynciionella, the aspect and condition of the shells of this genus are 

 quite different ; and the* geographical range of species of the two genera 

 is likewise very different, the Leiorhynchus having a more restricted 

 vertical and horizontal distribution. I have only to regret that all efforts 

 to develope and illustrate the interior structure have thus far proved 

 unsatisfactory. 



X. ON THE GENERA PENTAMERUS AND STRICKLANDINIA, AND 

 THEIR SUPPOSED RELATIONS WITH RENSSELiERIA. 



The essential points of this paper are presented on pp. 161-113, of this 

 report, and it will therefore be deferred till the illustrations are completed; 

 to appear in the next report on the State Cabinet. 



Correction. — The observations regarding Pentamerus lens were 

 based upon a species from Anticosti, identified with the European species 

 by Mr. Billings. An examination of the figures of the P. [Stricklandinia) 

 lens in Mr. Davidson's Monograph of Silurian Brachiopoda shows it to be 

 very distinct from the species which I examined under that name from 

 Anticosti. 



[Assem. No. 22>^.] 35 



