BRITISH FOSSILS. 



of the free cheek was prolonged into a genal spine. The labrum 

 is unknown. 



The body rings are few ? in number. The axis is rather wide and 

 more convex than the pleurae (epimerals). A deep groove passes 

 diagonally across them, curving slightly backwards from behind the 

 anterior and inner angle of each epimeral portion to the outer and 

 forwards to the outer angle.* The distal ends of the pleurae are 

 truncated obliquely forwards. 



Of the tail we have only a fragment, bufc enough to show that it 

 was somewhat triangular, marked with, many segments, but fewer 

 than in the tail of Dionide {Polytomurus of Corda). 



We reo'ard the structure of the head in SaUeria as intermediate 

 between that of Trinucleus and some of the Olenidce. We may 

 expect to find a series, beginning with the distinct facial suture and 

 crescentic eye of Bemopleurides, then the suture gradually approach- 

 ing the edge of the head, passing through its position in Scdteria, 

 Ampyx, and Gyphoniscus, till it reaches the edge in Dionide and 

 Trinucleus, the eye becoming more and more linear as it ap- 

 proaches the margin, till when it reaches it, the suture being 

 constantly immersed in mud, and its function in abeyance, it 

 becomes altogether obsolete, and is sometimes replaced by stemmata ? 

 jutting out on the epimerals of some of the other head segments. 



We have much pleasure in dedicating this remarkable genus to 

 our friend, lately the Palaeontologist to the Survey. 



Varieties. — The only, variations whicli we possess of this species 

 depend on age and size. Our largest specimen (fig. 1) may have 

 been about an inch in length. The glabella is slightly carinated on 

 the posterior third, and the longitudinal grooves are well marked. 

 In smaller examples the glabella ridge is absent, and the longitu- 

 dinal furrows scarcely perceptible. 



Locality and Geological Position. — We procured about half a 

 dozen specimens of the head from Schists forming the base of the 



Graptolite and Orthoceratite flags/' Penwhapple Glen, in the 

 Girvan district ; — the equivalents of the Upper Bala or Caradoc 

 Rocks.'" 



P. Wyville Thomson. 



* The groove is more forward than in our figure, so as to leave a larger posterior half 

 to the pleurae, but the direction of the groove is correctly given. 



