Belt — On the Fauna of the ^' Lingula Flags.'" 9 



P. flahella, have almost their exact counterparts ia the Lower 

 Tremadoc rocks of Dolgelly, although, as I have already shown, 

 there are 5,000 feet of strata lying between, occupied by an entirely 

 distinct fauna. 



When examining the nearly barren strata of the Maentwrog epoch, 

 I have sometimes speculated on the cause of the poverty of its fauna. 

 It was not on account of the nearness to the beginning of life on 

 our globe, for in older rocks still, a varied fauna abounded. It could 

 scarcely arise from conditions of sea bottom, for thick alternations 

 of sand, with fine grained sediments, bespoke varied depths of water 

 under which they had been deposited. The blue beds of the 

 Maentwrog strata do not differ lithologically from the blue beds of 

 the Menevian group. Might there not be in these ancient epochs 

 great oscillations of climate, such as we have certain proofs of in 

 more recent times ? Was it the advent of a cold period that drove 

 southwards the Lower Cambrian fauna, excepting a few modified 

 forms fitted to thrive in a more rigorous climate ? and was it the 

 return of a warmer climate in the Tremadoc epoch that brought 

 back the ancient types of life more or less changed ? 



NOTES ON THE SPECIES. 



Conocoryphe? Williamsomi, spec. nov. (PI. II. Figs. 7-11.) — Length 

 lj-2^in., breadth |-l|^in. Ovate oblong. 



Head, broadly semi-circular, with short strong spines pointing downwards and out- 

 wards. Glabella, a truncated cone, with two pairs of oblique furrows. Eyes small, 

 joined to the glabella by short prominent ocular ridges, and distant from it about 

 one-half its width. Frontal limb moderate, with a narrow margin. Fixed cheeks, 

 curving out below the eye. Free cheeks, broad, with a scarcely impressed margin. 



Thorax of 14 rings. Axis tapering, depressed. Pleurae, flat, first two, pointed and 

 strongly facetted, the remainder falcate and very slightly facetted, 



Pygidium of 4 axial rings, of which the last is pointed and ends in a narrow ridge, 

 running out to the margin of the limb. Limb rounded and slightly retuse, with 

 about four furrows. Margin depressed, broad next the pleurae and tapering to where 

 it meets the ridge from the last axial ring. 



The head of this species somewhat resembles C. depressa, Salter, but is easily dis- 

 tinguished from it by the deep glabella furrows, falcate pleurae and truncate, slightly 

 retuse tail. I know of no other species with which to compare it. 



I have great pleasure in dedicating this fine species to my friend Mr. Ezekiel 

 Williamson, in whose company it was first found by myself in 1865, in the black shales 

 of the Upper Dolgelly beds, near Rhiw-felyn. 



Conocoryphe f longispina, spec. nov. (PI. II. Figs. 12-14. — Length 

 Jin,, breadth Jin. Ovate. 



Head. — Head semi-circular, with long, slightly curved spines, reaching beyond the 

 tail. Glabella oblong, truncate, about as broad as long, with two pairs of deep, 

 oblique furrows, of which the lowest is most oblique, and reaches nearly to the neck 

 furrow. Eyes large, connected to the glabella by prominent ocular ridges, and 

 distant from it rather less than one-half its width. Frontal limb broad, with a 

 lineated margin. Fixed cheeks, minute. Free cheeks broad, with a lineated margin. 



Thorax of 14 rings. Axis regularly tapering. Axial rings, with a small tubercle 

 at each end, and traces of a central tubercle, which are more prominent on the 

 lower rings. Upper pleurae pointed, strongly facetted; middle pleurae falcate, 

 moderately facetted, lower pleurae truncate, slightly facetted : all bent down at less 

 than one -half their length from the axis, 



Fygidium sub-rotund, of three axial rings. Limb, with three furrows. Margin 

 narrow, linear. 



This species is easily distinguished by its long head spines ; short, broad glabella ; 

 long eyes and broad frontal margin. It occurs sparingly along with the last in the 

 . Upper Dolgelly beds, near Ehiw-felyn, where I discovered it in 1865. 



