100 BRITISH CAMBRIAN TRILOBITES. 



Tail small, semicircular, with an entire margin. Axis forming more than one- 

 third the total width, ending bluntly, divided into three rings and a terminal 

 portion. Lateral lobes with three fairly strong furrows, with a fine interlineation 

 between the first and second. 



Dimensions. — The specimen shown in Plate XII, fig. 1, which may be considered 

 of normal size, is 24 mm. long. The large glabella in Plate XII, fig 2, indicates a 

 total length of 37 mm. 



None of the specimens that I have seen show the tail perfectly, and I do not 

 feel sure that the margin is entire. The possibility of the presence of small points 

 is not altogether excluded. A feature that is worthy of note is, that the pleura? of 

 the first segment of the tail show a tendency to become more or less detached from 

 the rest. 



The principal characters by which the authors of this species distinguish it from 

 Peltura scarabatoides are the parallel-sided glabella, the very narrow free cheeks, 

 the punctations in the marginal furrow in front of the glabella, the entire tail, and 

 the form of the pleura?. As remarked above, it is not quite clear that the tail is 

 entire, and, in any case, it is usually very difficult to be certain on this point. The 

 punctations, too, are by no means always distinct. But the shape of the glabella 

 is usually clearly shown. The anterior angles are, as it were, somewhat pulled out 

 like the corners of a sack or cushion. In P. scarah&oides, on the other hand, the 

 glabella narrows slightly forwards and the anterior angles are rounded off. 



The body as a whole and the axis (including the glabella) in particular, are 

 less convex than in Swedish specimens of P. scarabseoides ; but this may be due 

 to pressure. The Malvern specimens of P. searabae.oides are quite as flat as 

 P. punctata. 



Raw 1 considers this species to be very closely allied to Triarthrus shinetonensis, 

 and is inclined to regard the two as forming a special section of the genus 

 Triarthrus. But in the number of thoracic segments and in the small size and 

 very forward position of the eyes, P. 'punctata is a typical Peltura and differs 

 altogether from Triarthrus. 



Horizon and Localities. — Tremadoc : Nant-y-caws, Nant-y-glasdwr, Nant-cwm- 

 ffrwd, and other localities near Carmarthen; Cwm-du, Llanarthney. 



3. Peltura olenoides (Salter). Plate XII, figs. 4, 5. 



1866. Conocoryphe ! olenoides, Salter, Mem. Geol. Surv., vol. iii, p. 308, pi. viii, fig. 6. 



Head subreniforu. Glabella convex, forming about half the total width of the 

 head, nearly parallel-sided, rounded in front, reaching the anterior margin; 

 neck-furrow rather broad and shallow, arched forwards in the middle line ; no 

 indications of lateral glabellar furrows. Eye small, placed very far forwards and 



1 Rep. Bnt, Assoc , 1907, p. 512. 



