10 



BRITISH FOSSILS. 



wliicli is half the length of the tail, not very strongly marked out, 

 and has a small anterior prominence. 



The Caradoc or Llandeilo flag species, A. limhatus, Salter, is 

 somewhat like it in the broad and somewhat duplicated border, but 

 differs in the much smaller axis, and more backward position of the 

 central tubercle. Our species, imperfect as it is, is distinct from 

 and lies midway between this species and the Bohemian A. nudus, 

 a primordial form. 



Locality and Geological Range. — Lower Llandetlo (Arenig 

 group). Tai hirion, west of Bala, collected by J. W. Salter in 

 1853. 



Section 1. — Agnostus? 



AGNOSTUS TRISECTUS. 



Plate I. Fig, 11. 



Diagnosis. A. cauda suhrotunda ijiermi, axi longo trilobato^ multi- 

 segmentato. Axis fere percurrens, latus, ad medium constrictus et tuher- 

 culatus^ sulcisqite longitudinalibus binis approximatis exaratus. 



Two specimens only have been sent to Mr. Tennant of this rare 

 species. It is very like A. princeps, from which it differs, at first 

 glance, by the central narrow ridge on the axis, running down 

 throughout its whole length. It is, besides, apparently a flatter 

 species, and has no trace of the posterior spines, but in their place 

 a simple swelling of the margin on each side. This character is 

 unusual. 



It is a sm-all species, the tail not being above a line and a half in 

 diameter. It is about as broad as it is loug, much rounded in out- 

 line, very slightly convex, but the flatness may perhaps be due to 

 pressure. The axis is very broad, and the basal lobes — those next 

 the thorax — are broader and longer than usual, and nearly equal 

 and similar to the second lobe of the axis. The large terminal ovate 

 lobe is longer than the other two put together. All three are deeply 

 divided along the middle line by a pair of parallel furrows, v/hich 

 divides the axis into three strong lobes ; hence the trivial name. 



Locality and Geological Position. — Upper Lingula Flags. 

 Black Shales of Whiteleaved Oak, Malvern. Probably not un- 

 common ; it is a conspicuous species. 



