BY R. ETHERIDGE, JUN., AND JOHN MITCHELL. 503 



semi-circular, anterior or thoracic margin straight, with a strongly 

 marked axal facet ; axis somewhat deltoid, sub-conical, or sub- 

 triangular, less than one-fourth the length of entire pygidium, 

 simulating about seven or eight obscurely subdivided segments ; 

 edges emarginate ; pleurae convex at their inner ends, becoming 

 compressed outwardly, gradually widening from behind forwards ; 

 central, or axal pleura widest and undivided ; inter-pleural grooves 

 well marked, each pleura strongest along its inner margin ; trans- 

 versely concentrically crenated, also with a number of indented 

 lines traversing the medial part of the surface ; limb flat, and 

 moderately wide and striated sub-concentrically. 



QJjs, — In comparing this with other described species, we may 

 at once dismiss all those possessing a bifurcate median pleura in 

 the pygidium, which in B. Jenkinsi is entire. We believe this 

 species to be that referred to by de Koninck as B. Partschi, Ban*., 

 and it certainly is the form figured by Jenkins without specific 

 name, although he distinctly called attention to the resemblance 

 of his fossil to the above species. In the first place B. Jenkinsi 

 acquired much larger dimensions, as a rule, than B. Partschi, one 

 of the pygidia of our species being equal to the entire length of 

 the body in the Bohemian Trilobite. In the second place, the 

 much stronger aiid better marked glabella furrows, the more 

 definite segmentation, and dissimilar axis of the tail, and probably 

 the more intricate ornamentation of the test separate the species. 

 It further differs in possessing a much squarer pygidium, arising 

 from the straight sides, and in this character there is also a marked 

 discrepancy from the structure of such species as Bronteus 

 Edwardsi, Barr., B. planus, Corda, B. Brongniarti, and others. 

 On the other hand Bronteus Jenkinsi resembles B. Partschi in the 

 forward extension of the glabella and the near equality in width 

 of the thoracic axis to the pleurae. 



On examining a number of specimens we find that the thoracic 

 axis is about one-sixth wider than the pleurse, especially in large 

 examples ; but in two medium-sized specimens the relative widths 

 practically agreed. We also find that the proportionate length 



