378 TWENTIETH REPORT ON THE STATE CABINET. 



Formation and locality. In limestone of the Niagara group, at Wauwa- 

 tosa ; and a single specimen of doubtful locality, received from Mr. I. A. 

 Lapham, has the aspect of the Bridgeport rock. 



ILL^NUS lOXUS (n.s). 



PLATE 22 (13), FIGS. 4-10. 



lUanus barriensis, page 332 (28) . 



'' '' Pal. N. Y., Vol. ii, pa. 302, pi. 66. 



Probably not identical with /. barriensis of Murchison, Silurian System. 



There are several slight differences between the American (Wisconsin) 

 specimens referred to this species, and the figures and descrip ' of the 

 English form of I. barriensis^ as given in the British Decade 2, pi. 3 and 4. 

 None of these differences, however, appear to be very important or strongly 

 marked. On the head the eye is placed a little more obliquely ; the mova- 

 ble cheek is comparatively longer from the posterior angle to its anterior 

 margin ; the facial suture lines unite with the rostral suture, forming an 

 abrupt angle instead of a rounded one ; the rostral shield is proportionally 

 narrower from side to side, especially on the inner margin, where it unites 

 with the hypostoma. 



The differences in the pygidium are not readily observed. We have no 

 means of comparing the articulations of the throax in the Wisconsin 

 specimens. 



The New- York specimens usually referred to I. harrie^isis have the same 

 form of head and pygidium as those of Wisconsin, and differ from the 

 figures of the British species in the direction of the terminations of the 

 pleura. Notwithstanding the differences are not conspicuous, I am inclined 

 to regard them as of the same importance as those which distinguish 

 closely allied species. 



The accompanying outline figure shows the direction of suture lines and 

 form of rostral shield in this species of Ill^nus. 



