702 SILURIAN TRILOBITES, 



As regards 0. Leonhardl, with which Mr. Ratte compared this 

 fossil provisionally, the two are unquestionably near one another. 

 Mr. Ratte appeared to think that a greater breadth existed in 

 the fixed cheeks of the Australian fossil; but we would rather 

 rely on other characters of possible specific value. For instance, 

 the spines of our form are much longer and stouter than those of 

 0. Leonliardi, the anterior ones of ours, too, are always fleeted 

 backwards at a greater angle; the genal spines at their bases press 

 on the two anterior pairs of the thoracic pleurte, and these two 

 pairs of pleurae have very rudimentary spines, which is a feature 

 of itself that clearly separates it from 0. Leonhardl and its 

 congeners. The frontal margin of the glabella of 0. Raltei is 

 spined or serrated, but the margin of 0. L''onhardi is smooth. 

 The pleural spines are moi'e graduated in length from before 

 backwards, producing a remarkable frill-like appearance in 0. 

 KiMei, whilst the characters of the pygidium are very distinct. 

 In 0. Lfionhardi, between the axial or pleural spines are four 

 peripherals, and exterior to the former two peripheral spines on 

 either side. In 0. Ratlei, on the other hand, there are in a typical 

 specimen two peripheral spines occupying the first position and 

 four to five the second; but in another typical specimen (immature) 

 there are two peripherals in the first and three to four in the 

 second position. We have never seen three spines on the 

 pygidium of 0. Rattei between the axial or pleural spines, and 

 it is wider and the spines larger, longer and more unequal in 

 length than is the case with those of 0. Leonhardl. 



The normal number of spines that can be seen on a pygidium 

 of 0. Rattei when attached to the thorax is ten, and the actual 

 number twelve, the one on each angle being mostly very rudi- 

 mentary, and in some specimens bifurcate. In cases such as the 

 latter, a tail may bear fourteen spines, but not more than ten 

 would probably be visible if the fossil were complete. 



Odontopleura pigra, Barr., sp.,* is so far related to the present 

 species that although the pleural spines of the first two thoracic 



Novak, Dames & Reyser's Pal. Abh. 1S90, v., Heft 3, t. 2, f. 11 & 13. 



