D)'. Ivor Thomas — Trilohitc Fauna of Devon and Corincall. 197 



Permian), Avith its subgenera Griffithides, PsendophUlipsia, Brachj- 

 mefopus (Carboniferous), and Bechenella (Devonian). Oehlert (12, 

 p. 127), however, gives a slightly different division of the group. He 

 separates the forms into two sections : Section A, Proetidas, with 

 glabella tapering anteriorly and including the genera Proettis, 

 Bechenella^ and Brachymetopus, together with Phmton (Silurian), a 

 subgenus of Proctus ; Section B, Phillipsidse, with the glabella 

 widening anteriorly : these include the genera Phillipsella (Silurian) 

 and Phillipsia, together with Griffithides as a subgenus of the latter. 

 In a later note (12, p. 141) Oehlert withdraws the name Phillipsella 

 in favour of Novak's PhiUipsindla^ which had priority. 



Proetus dunhevldensis, sp. nov. PI. VII, Fig. 6. 



Bescription. — The general shape is elongate oval, the margins 

 bordering the thorax longitudinally being sub-parallel. The total 

 length is 17'5mm. approx., the breadth at the centre of the thorax 

 being about 11 mm. In profile there is a sharp rise from the 

 posterior border of the pygidium to the hindmost ring of the thorax, 

 and from this point there is a gentle downward slope to the glabella. 

 The slope forwards along the surface of the glabella is steeper and 

 more like that of the pygidium until the frontal margin is readied, 

 where a somewhat .sharper fall towards the marginal border occurs. 



The cephalon is obtusely parabolic, the breadth being slightly more 

 than twice the length. The anterior margin is regularly convex, 

 while the posterior boundary is slightly concave to the thorax. The 

 genal angles are produced into long, gradualh* tapering spines, one of 

 which is tiaceable to the seventh pleuron of the thorax. 



The glabella is elongate oval, slightly narrowing towards the 

 rounded anterior end. The ratio of the length to the greatest breadth 

 is about 5 : 4. Under strong magnification there is an indication of 

 three faint furrows on either side, two of which occur close together 

 on the margin near the anterior end of the eye, while the other runs 

 inward and backward from a point near the middle of the eye, 

 separating off a small indistinct basal lobe. The occipital furrow is 

 fairly deep and narrow, and bounds a well-marked occipital ring. The 

 latter arches forward in the centre and is slightly rounded, and 

 approximately the same width as the thoracic axial rings. In front of 

 the glabella and continued down to the gonal spines on either side is 

 a well-marked apparently flattened border which gradually narrows 

 anteriorly. Owing to lateral compression, which has affected most of 

 the left side of the specimen described, this border is imperfect to the 

 left, but is better preserved and more of the natural width to the right 

 of the glabella. 



T\\cji.ved cheeks are elongated and narrow, with a triangular, roughly 

 equilateral, anterior and a narrower, also triangular, posterior portion. 

 The eye-lobe is comparatively low and not prominent. The facml 

 sutures cut the anterior border of the head-shield at a distance from 

 Que another slightly greater than the length of the glabella. They 

 run gradually inwards posteriorly from their anterior terminations, 

 then curve outwards round the eye-lobe, and Tiltimately cut the 

 occipital ring obliquely at a low angle, reaching the posterior margin 



