490 SILURIAN TRILOBITES OF NEW SOUTH WALES, vi., 



Crotalocephalus SILVERDALENSIS, sp/JWV. 

 (Plate xxiv., fig.lO: Plate xxv., %s.l-3 and 9). 



Sp. CArt?'5.— Complete form straight-sided, ovate. 



Cephalon semicircular and only gently inflated, length a little 

 less than half the width between the genal angles. Glabella 

 suhquadrate or subpyriform, large, finely granulate, very moder- 

 ately tumid, highest centrally between the first and second pairs 

 of lateral furrows; frontal lobe large, spindle-shaped or sub- 

 elliptical, second and third pairs of lobes very openly V-shaped, 

 continuous, basal pair circumscribed, but joined by a low ridge 

 on which are four to six small tubercles: lateral furrows con- 

 tinuous, deep, wide, widely V-shaped : neck-furrow centrally 

 wide and deep, more or less communicating with the third 

 lateral furrows, very narrow behind the basal glabella-lobes; 

 neck-ring wide, strong, centrally arching anteriorly; axial grooves 

 narrow but distinct; fixed cheeks, practically obsolete in front of 

 the eyes, being represented b}' a very narrow band on which the 

 free cheeks rest, posteriorly large, subtrapezoidal, depressed, 

 beautifully and coarsely punctated; posterior and lateral furrows 

 very distinct; posterior borders strong; genal angles bearing 

 short claw-like spines; eyes small, close to the axial grooves, and 

 opposite the second glabella-lobes; facial sutures from the pos- 

 terior angles of the eyes run straightly at angles of 75° to 80' 

 with the axial centre-line to the lateral margin, but, anteriorly, 

 they follow the glabella-boundary to the frontal angles, thence 

 inwards and pass out medially; free cheeks have not been found 

 in position. 



Thonix quadrate or suboblong, of eleven somites, length about 

 five-sixths of the width between the genal angles, width, in- 

 clusive of the spines, equal to the distance between these same 

 angles; depressed, whole surface finely granulate; axis depressed, 

 much wider than the pleural lobes exclusive of the spines, about 

 two-sevenths of the greatest cephalic width; six anterior rings 

 practically equal in width and very slightly wider than the neck- 

 ring, the remainder contracting very gradually to the pygidinm, 

 but little arched: the tenth and eleventh more strongly than the 

 rest; axial grooves narrow but distinct; pleural lobes of the 



