IS BRITISH CAMBRIAN TR1L0BITES. 



of the restored free cheeks along the line of the inner parts of the back of the 

 fixed cheeks. 



" The form here described differs somewhat from Brogger's and Moberg's 

 figures and descriptions of the species. In these the anterior part of the glabella 

 appears round and well defined, seeming to rise abruptly from the frontal limb, 

 while in the Shineton form the anterior part of the glabella is low, descending 

 gently to the front. Again, neither Brogger nor Moberg mentions the prominent 

 pits which limit the extent of the axial furrows in front. The writer is assured, 

 however, by the author of this monograph, who has seen Scandinavian specimens, 

 that it is identical with that species. 



" It may be remarked here that the detached tails figured by Moberg probably 

 do not belong to this genus." 



The fact that I have seen Scandinavian specimens does not entitle me to 

 express an opinion without giving the reasons upon which that opinion is based ; 

 nor would I venture positively to assert the identity of the British and Scandi- 

 navian forms until we know more about the latter than Ave do at present, for it 

 sometimes happens in Trilobites that specific distinctions lie not in the head but in 

 the tail and thorax. I do not think, however, that the differences pointed out by 

 Mr. Raw are sufficient to characterise a new species. The pits at the anterior 

 ends of the axial furrows have no diagnostic value, for they are common in 

 Am/pyx, Trinucleus, Oalymene, and other genera, but are not usually visible except 

 in well-preserved specimens. A more important difference is the comparative 

 flatness of the glabella in the Shineton specimens. These, however, occur in 

 shale, while the Scandinavian specimens are found in calcareous beds ; and it is 

 very common to find forms preserved in shale with very much flatter and less 

 prominent glabellas than the same species in a limestone band. It is, then, to 

 differences in the mode of preservation that I attribute the differences between 

 the British and Scandinavian specimens. 



Horizon and Localities. — Upper Tremadoc : Shineton; Arenig ? Most of the 

 specimens of Orometopus from the Arenig district are specifically indeterminable. 

 0. praenuntins undoubtedly occurs, but some of the specimens may belong to 

 0. elatifrons. 



2. Orometopus praenuntius (Salter). Plate IV, fig. 11. 



1866. Ampyx pnenuntius, Salter, Mem. Greol. Surv., vol. iii, p. 321, pi. viii, fig. 5. 



General form depressed, circular. 



Head semicircular, with the genal angles produced into long spines. Glabella 

 subquadrate, wide in front, narrower behind, about three quarters the length and 



