78 BRITISH CAMBRIAN TRILOBITES. 



Tail sub-triangular, but with the apex very much rounded, width rather more 

 than twice the length, margin entire. Axis wide, forming about two-fifths of the 

 total width, consisting of three segments, terminating bluntly, not quite reaching 

 the posterior margin. Lateral lobes rather narrow, with a faint furrow near the 

 anterior margin. 



Dimensions. — In the specimen figured in Plate VIII, fig. 9, the cranidiuin is 

 about 3 mm. long and nearly 5 mm. wide at the eyes, the head and thorax together 

 8 mm. long. 



This species is very closely allied to Sph&rophthalmus alatus and is distinguished 

 chiefly by the relatively narrower axis and wider lateral lobes throughout the body. 

 The head has the fixed cheeks nearly as wide as the glabella, while in S. alatus they 

 are little more than half that width. The tail is wider in proportion to its length 

 than in 8. ala/us, but the extra width lies in the lateral lobes ; in shape it is more 

 rounded, and the axis also terminates more bluntly. It is in the thorax that the 

 resemblance between the two species is closest; but even here the axis appears to be 

 relatively narrower than in 8. alatus. Unfortunately in both forms the ends of the 

 pleuras are usually buried in the matrix and the width cannot be determined. S. 

 major is generally larger, and the fulcrum appears to lie somewhat further out than 

 in 8. a hit us. 



Sph. majuscuhis, Linnarsson, 1 bears a considerable resemblance to 8ph. major. 

 The head which Linnarsson ascribes to that species has the fixed cheeks as wide as 

 the glabella ; but the tail, on which the species was founded, is triangular instead 

 of rounded; the axis is more pointed than in Sph. major, anjd consists of four 

 segments instead of three. 



Horizon and Localities. — LTpper Lingula Flags: Malvern; Moel Gron. 



Genus CTENOPYGE, Linnarsson. 



The genus Gtenopyge was founded by Linnarsson - for the species Gtenopyge 

 pecten, and was separated from Spliaeropldhalmus mainly on account of the char- 

 acters of the tail. In Sphserophthahnus the tail is small, triangular, with an entire 

 margin, and with an axis consisting of only a few segments; in Gtenopyije the tail is 

 large, with a multi-articulate axis, and the side-lobes consisting of several segments 

 which are quite distinct from one another and which end in backwardly directed 

 spines. According to Linnarsson the head is similar to that of Sphxrophthahrms, 

 but with wider fixed cheeks, especially behind the eye ; the axis of the thorax is 

 narrower and the pleurae are produced into reflexed spines. 



Unfortunately Ct. pecten is the only species of which the tail is known ; and in 



1 Geol. Foren. Stocldi. Forh., vol. v (1880), p. 141, pi. v, figs. 11, 12. 



2 Lot: cit., vol. v (1880), p. 145. 



