104 BRITISH CAMBRIAN TRTLOBITES. 



by Walcott 1 the type of a new genus, Protypus, shows many points of resemblance 

 to B. depressa. The general shape is similar, the glabellar furrows are obsolete, 

 the number of thoracic segments is the same, the pleural grooves are of the same 

 character, and the tail is small and entire. But the ocular ridge is much more 

 strongly marked, and the facial suture is described as cutting the margin at right 

 angles. In his first notice Walcott ascribes the species to the Middle Cambrian, 

 but in his later work he includes it in the Olenellus fauna. 



The divergent course of the anterior branches of the facial suture distinguishes 

 Beltella from all the other genera of Olenus sensu lato except Parabolinella. In 

 the latter genus the general form is flatter and the number of thoracic segments 

 greater, the glabella is usually more truncate and the glabellar furrows much more 

 sharply defined, and the frontal limb is wider. 



1. Beltella depressa (Salter). Plate XII, figs. 6 — 10. 



1859. Ellipsoeephalus depressns, Salter, Murohison's Siluria. 2nd edn., 3 p. 47, Foss. 7, fig. 2. 



18(56. Conocoryphe (Solenopleura ) depressa, Salter, Mem G-eol. Surv , vol. ill p. .307, pi. vi, figs 1, 2. 3. 



? 1866. Conocoryphe vexata, Salter, ibid., p. 307, pi. viii, fig. 7. 



Head semicircular, with the genal angles produced into spines. Glabella 

 quadrate, broadly rounded anteriorly, narrowing slightly towards the front, sepa- 

 rated from the marginal furrow by a space about equal to the marginal rim in 

 width ; with two pairs of glabellar furrows, of which the first is almost obsolete 

 and the second distinct, very oblique, reaching nearly to the neck-furrow ; neck- 

 furrow strong. Eyes small, placed a little nearer to the anterior than to the 

 posterior margin, at a distance from the glabella less than half the width of the 

 latter, with a very indistinct oblique ocular ridge running towards the anterior 

 angles of the glabella. Facial suture apparently running very obliquely outwards 

 across the margin, thence inwards to the eye and thence outwards to the posterior 

 margin, which it cuts at a distance from the glabella about equal to two-thirds 

 the width of the neck-segment. Fixed cheeks narrow at the eyes, widening both 

 in front and behind ; free cheeks fairly wide, with a broad margin which is pro- 

 longed at the angles to form the backwardly directed genal spines. 



Thorax consisting of twelve segments, varying but little in width as far as the 

 seventh segment, tapering rapidly behind. Axis forming rather less than one- 

 third of the total width except in front. Pleuraa with the fulcrum placed more 

 than half-way out, straight and horizontal up to the fulcrum, and then bent slightly 



1 Bull. U.S. Geol. Surv., no. 30 (1886), p. 211, pi. xxxi, fig. 4; Tenth Ann. Rep. U.S. Geol. Surv. 

 (1890), p. 655, pi. xcviii, fig. 6. 



» Called on the title-page — Third Edition (including "The Silurian System"). 



