504 ME. W. B. R. KIXG OX THE [vol. lxxix, 



The fauna of the lowest Ashgillian is that of the Rhiwlas 

 Limestone and Mudstone ; but, in tlie higher Ashgillian beds, the 

 fauna is much richer than in the western parts of North Wales, 

 and it is here that several new forms of interest are found. 



It will be noticed that, in the lists of fossils from the Calymene- 

 quadrata Beds a large number are identified with forms found in 

 the 'Starfish Band' of the Drummoek Group at Girvan. 



The fauna of the Triiiucleus-hucltfandi Mudstones appears to 

 belong to the Caly mene-quadrata fauna, and not to the Pliacops- 

 mucronatus fauna. 



The stratigraphical evidence for placing the Meristina-crassa 

 Sandstone in the Silurian has already been noted ; but, from the 

 point of view of the fauna, there are difficulties. If, however, 

 Miss Elles's contention as to the age of the Hirnant Beds be 

 admitted, then there would be little doubt that the M.-crassa 

 Sandstones are also Silurian ; for the species (apart from new 

 forms) are either found in the Hirnant Beds, or in the normal 

 Lower Yalentian. On the whole, therefore, the evidence in this 

 area supports the ascription of a Silurian age to the Hirnant Beds. 



Description of Fossils. 



Calymexe quadrata sp. nov. (PL XXYI, figs. 1 & 2.) 



Description. — The general outline is that of a roundly trun- 

 cated inverted cone. The head-shield is a quarter of the length 

 of the whole, and presents the general appearance of being wide and 

 short. The glabella is inflated, and its width, from the outside of 

 the basal lobes, is equal to, or somewhat greater than, its length ; 

 while the quadrate form of the frontal portion is sufficiently 

 distinctive to suggest the name quadrata. The whole surface 

 shows a fine granulation, which is equally developed on young 

 and on adult individuals. The basal glabellar lobes are large and 

 round, while the second and third lobes are much smaller and of 

 nearly equal size. This circumstance, together with the extreme 

 straightness of the anterior margin of the glabella, accounts for 

 the almost square outline of the anterior half of the glabella. 

 The frontal border is of the concave flattened type (as in 0. plani- 

 marginata Keed) ; but, owing to the inflated nature of the 

 glabella, the margin only, rises to about half the height of the 

 glabella. The anterior margin, when seen from above, is straight, 

 or even slightly incurved towards the glabella. The eyes are 

 small, situated opposite the second glabellar lobe, and raised to 

 about the same height as the glabella, thus leaving a deep, slightly 

 concave, axial furrow between the raised fixed cheek and the 

 glabella. A marked pit is observable in the axial furrow, somewhat 

 in front of the third glabellar lobe. The rostral suture is seen to 

 run just on the under side of the raised frontal margin to a 

 position immediately in front of the eye ; the anterior part of the 

 facial suture joins this point to the eye in an almost straight line. 

 At the eye, the lateral part of the facial suture makes a right 



