Victorian Fossils, Part XIV. 299 



within the section Trimerus of Green. In general form it closely 

 approximates to H. delyliinocephalu8 of the wool hope and 

 wenlock limestone of England, and the Niagara limestone of 

 North America. It differs, however, from that species in the 

 shape of the anterior part of the cephalon and in some minor 

 details. 



In general form H. vomer is elongate or long ovate, broadest 

 at base of cephalon, tapering to a point behind ; back depressed 

 convex, with deflected sides. Cephalon triangular, acuminately 

 arched in front with a strongly depressed surface^, granulate ; 

 glabella subtriangular, truncated anteriorly, with a central, 

 longitudinal crest and three pairs of furrows trending upwards 

 and outwards. Eyes prominent, distant, a little more than half 

 the width of the cephalon. Neck furrow sharply defined in the 

 middle axal region, and by a broader depression at the base of 

 the fixed cheeks. 



Thoracic segments well defined, about thirteen ; axal furrows 

 broad, pleura bending sharply down at the fulcra. 



Pygidium long and slender, more acutely pointed than in 

 K. delphinocephalus. Surface of carapace finely granulate. 

 Judging from the type specimen, the power of enrolment was 

 great. Although not so long as its nearest ally, H. delphi- 

 nocephalus, this species must have been a handsome form when 

 living. 



Dimensions. — Type specimen. Length of cephalon, 32.5 mm. ; 

 width of cephalon, 46 mm. ; length of glabella, 18 mm. ; width 

 between eyes, 27 mm. 



From another specimen of similar size. Length of thorax, 

 59 mm. ; w^idth of thorax, 43 mm. ; width of pleura in middle 

 of thorax, 4.5 mm. ; length of pygidium about 38 mm. 



Occurrence. — Silurian. Wandong, Victoria. Type specimen 

 presented by Mr. J. T. Jutson. Paratype presented by Mr. G. 

 Sweet, F.G.S. A cephalon of a young specimen (additional 

 paratype), presented by Mr. F. P. Spry. 



1 Reminding one of a ploughshare, hence the specific name. 



Sa 



