I)r. F. R. Coivper Reed — The genius Homfialonotus. 323 



Examples. 



H. Sedgivicki, Salter. H. ascriptus, Reed. 



H. Edgelli, Salter. ' ? H. rudis, Salter. 



H. Taivneyi, sp. nov. 

 Ukmarks. — It was to this group that Salter first applied the name 

 Brongniartia^ choosing H. bisulcatus as the type-species. The 

 differentiation in. structural characters from Synhomalonotiis is much 

 more marked than in Eohomalonotus, particularly in the pygidium, 

 and all the members of this third subgenus occur on higher horizons 

 than those of the first subgenus, to which it is, however, closely 

 related. 



4. Irimerus, Green. 



Head-shield more or less triangular and elongated. Facial sutures 

 uniting anteriorly close to but inside margin in a more or less 

 pointed arch, not forming a continuous regular curve, and posteriorly 

 cutting genal angles. Pre-glabellar area well developed. Glabella 

 subconical, occasionally lobed. Thorax with very broad axis and 

 indistinct trilobation. Pygidium composed of many segments, 

 triangular, elongated, subcjdindrical, ending in a produced acumina- 

 tion ; trilobation faint; doublure very narrow at sides, widening 

 at tip. 



Type. — H. delphinocephahcs (Green). 



Eange. — Silurian (Wenlock). 



Distribution. — Northern Europe, North America, Australia. 



Examples. 

 H. cylindricus, Salt. H. vomer, Chapman.^ 



if, Harrisoni, McCoy. 

 Kkmaeks. — Though in point of stratigrapliical succession this sub- 

 genus follows immediately on that of the H. hisulcattis type, yet the 

 pygidium represents an almost entirely new and independent form, 

 and the facial sutures show by their angular junction in front the 

 nature and origin of the continuous curved commissure in the earlier 

 sections. There is no direct derivation from the Ordovician forms, 

 but perhaps links, though at present undiscovered, existed in 

 Llandovery times. 



5. Kmiigia, Salter. 



Head-shield transverse, broad, short. Epistome projecting in 

 front as median process; anterior lateral angles of head-shield 

 angulated forwards, the three together making the margin tricuspid. 

 Facial sutures bending suddenly inwards near anterior margin and 

 uniting in a straight or concave transverse commissure with small 

 median point; posterior branches of facial sutures bent back suddenly 

 to cut lateral margins nearly at genal angles. Paraglabellar areas 

 distinctly marked. Pre-glabellar area very narrow. Thorax with 

 trilobation almost obsolete ; axis very broad, scarcely defined. 

 Pygidium composed of many segments, elongated, acuminate, 

 triangular, with smooth pointed posterior process; axis nearly 



' Chapman, Proc. Roy. Soc. Victoria, vol. xxiv, N.S., pt. ii, p. 298, pi. Ixii, 

 figs. 2, 3 ; pi. Ixiii, fifis. 1, 2, 1912; Etheridge <fe Mitchell, Proc Linn. Soc. 

 N.S.W., vol. xlii, pt. iii, p. 506, 1917. 



