6 



BHITISH FOSSILS. 



(1851), Pal. Foss. Woodw. Mus. pi. 1 E., fig. 11 [not of Corda] ; Agn. 

 McCoijii, Salter (1854), in Morris's Catal. Brit. Foss., 2nd ed.; id., Mem. 

 Geol. Siirv., vol. 3 (iued.), pi. 13, fig. 8. 



A very frequent fossil in the black Llandeilo flags of Builth, in 

 Radnorshire, but, as far as I know, not found elsewhere. It 

 accompanies the Ogygia BucJiii and Ampyx nudus, figured in a 

 former decade, and seems, like many others of the genus, to have 

 delighted in a habitat of black carbonaceous mud^ now converted 

 into shale. 



Description. — A minute species, never half an inch long, even 

 when head and tail are taken together (the body rings have not 

 yet been found). The head is rounded, not oblong, forming about 

 two-thirds of a circle, the base being contracted where it joins the 

 thorax. The tail is nearly of the same shape, a little more oblong. 

 In both the convex limb is nearly equal all round, and the glabella 

 and caudal axis are short and obtuse. The outer marginal rim is 

 narrow but prominent all round, and the two short marginal teeth, 

 are placed far back on the caudal border. 



The general shape thus given, we may notice a few details. The 

 glabella in front is remarkably broad and obtuse, always as broad, 

 and sometimes (fig. 7) broader than in the hinder moiety. A curved 

 depressed line separates the front portion from the hinder lobe, and 

 the two portions are about equal in length. The basal lobes are 

 small and inconspicuous. 



The limb is gently convex, and slopes equally on all sides away 

 from the central lobe, from which a sharp furrow separates it all 

 round ; one or two faint depressed radiating lines occur on the 

 limb. The margin is strong and continuous, but narrowest poste- 

 riorly, where it ends on each side with a projecting tubercle or 



minute SDine. The small basal or neck-lobes are transverse, 

 i. 



Body rings unknown. (They might surely be found at Builth by 

 collectors.) Tail of the same shape as the head, broadest posteriorly, 

 margined all round distinctly, and with a pair of spines which occur 

 on the sides, so far back as to be on a level with the hinder margin. 

 The axis is short and obtuse, not reaching much above halfway down 

 the tail, and leaving a broad equal limb. The axis is divided very 

 unequally by a transverse line into an upper and a lower lobe, at 

 the junction of which is the prominent tubercle characteristic of the 

 genus. The lower or terminal lobe of the axis is as broad as long, 

 the upper lobe twice as broad as long ; a pair of minute lateral 



j0'' 



