fc6 BRITISH CAMBRIAN TRILOBITES. 



I owe to the kindness of Mr. Fearnsides. It appears to be the form originally 

 described by Salter as Ampyx prasnuntius. 



Briefly, the genus resembles Ampyx, except in the following characters : The 

 glabella is not so large and does not reach to the frontal margin; well-developed 

 compound eyes are present ; there is a facial suture, which is marginal in front, 

 runs backwards to the eyes, and thence outwards and backwards to the posterior 

 margin ; the head is surrounded by a raised marginal rim ; and the number of 

 thoracic segments is usually more than six. It is in the characters of the tail and 

 the thoracic pleura? that the resemblance to Ampyx and Trinucleus is most striking, 

 while the presence of eyes and of a facial suture constitute the most important 

 differences. 



1. Orometopus elatifrons (Angelin). Plate IV, figs. G — 10. 



1854. Holometopus ? elatifrons, Angelin, Pal. Scand., p. 90, pi. xli, figs. 17, 17 a. 

 1882. Holometopus? elatifrons, Brogger, Die Silur. Etagen 2 unci 3, p. 128, pi. iii, fig. 13. 

 1896. Orometopus elatifrons, Brogger, Nyt Mag. f. Naturv., vol. xxxv, p. 68, note. 

 1906. Orometopus elatifrons, Moberg and Segerberg, Ceratopygeregionen, p. 99, pi. vii, fig. 3 (? non 

 fig. 4, 5). 



As this is another form to which Mr. Raw has devoted much careful study I 

 quote his manuscript description : 



" General form approximately circular. 



" Head crescentic, slightly angulated in front, extremely broad ; posterior 

 and lateral angles continued into long, somewhat diverging genal spines. 

 Glabella prominent, broadest about the mid-length of the shield, narrowing 

 behind, where it is strongly arched into a keel and continued as a strong spine 

 over the neck-segment and the anterior segments of the thorax, slightly narrowing 

 in front where it is rounded and descends gently to the broad marginal furrow. 

 Neck-segment well defined, narrow, bowing out behind under the spine. At a 

 distance in front of the neck-segment about equal to its width, faint, short 

 furrows, inclining up to the back, indent the sides of the glabella, and there are, 

 perhaps, indications of another pair at an equal distance in front. Axial furrows 

 well defined, ending in front in two rounded pits on either side of the glabella at 

 about a quarter the length of the head-shield from the front. Posterior furrows 

 on the cheeks broadening outwards and ending in two marked depressions. 

 Cheeks rising towards a sharp marginal ridge, bevelled outside ; ornamented 

 externally, except in the furrows, with a network of narrow ridges surrounding pits, 

 or in moulds of the inner surface with scattered pits. From the sides of the 

 glabella ;it its broadest part elevated eye-lines run outwards and somewhat back- 



