OROMETOPUS PR.ENUNTIUS. 49 



one quarter the width of the head, bounded by well-defined axial furrows, and in 

 front by a strong furrow separating it from the frontal limb ; neck-furrow distinct, 

 but no definite glabellar furrows. Cheeks wide, moderately convex, sometimes with 

 a prominent ridge extending from the anterior corners of the glabella to the genal 

 angles ; united in front of the glabella by a prominent frontal limb ; occipital 

 furrows strong ; a small lobe separated off from the cheek in the angle between 

 the axial and the occipital furrows. Eyes crescentic, placed near to the occipital 

 furrow, and about halfway between the glabella and the external margin. Facial 

 suture marginal or infra-marginal in front ; running nearly straight backwards to 

 the eye, then outwards to the marginal rim, and finally backwards and a little 

 inwards to the posterior margin. Margin forming a narrow raised rim, uniform in 

 width, striated on the doublure. Genal angles produced into long slender spines, 

 which curve at first a little outwards and then backwards, extending far beyond 

 the tail. 



Thorax of seven, or sometimes fewer, segments, narrowing slightly towards the 

 posterior extremity. Axis forming nearly one third of the total width in the first 

 three segments, narrowing posteriorly. Pleura? straight, horizontal, grooved, the 

 first three terminating in blunt points, the rest truncate and apparently bent 

 downwards at the tips. 



Tail wide but very short, forming a flat triangle. Axis narrow, conical, 

 reaching nearly to the posterior margin, showing traces of four rings. Lateral 

 lobes flat, with a very faint furrow near the anterior margin. Margin bent down- 

 wards. 



The largest specimens attain a length (exclusive of the genal spines) of nearly 2 cm. 



This species is closely allied to 0. elatifrons, and the differences are probably 

 even less than they appear at first sight, and are due in part to the less perfect 

 preservation of the specimens. In the specimen figured the glabella is more 

 quadrate than in the Shineton form and is not produced posteriorly into a spine, 

 but it is somewhat flattened by pressure, and other specimens from the same 

 locality suggest, though they do not prove, that the glabella was not very different 

 in shape from that of 0. elatifrons, and was perhaps produced posteriorly in a 

 similar fashion. There are, however, other differences which appear to be real. 

 In 0. elatifrons the space in front of the glabella, between it and the raised marginal 

 rim, is concave ; in 0. prspnuntius it is convex, and is separated from the glabella 

 by a distinct furrow. The ridges which run across the cheek from the anterior 

 corners of the glabella to the genal angles are absent in 0. elatifrons, but they are 

 not always very distinct even in the present species. 1 The genal spines in 



1 These ridges are similar to those described and figured by Salter in Trinucleus gibbtti (Mem. 

 Geol. Surv., vol. iii, p. 319, pi. xii, fig. 10), and, as appears to be the case in that species, are probably 

 only the result of lateral pressure acting upon a rather abrupt bend. 



8 



