RAYMOND: NEW AND OLD SILURIAN TRILOBITES. 37 



of the head. The glabella expands rapidly forward, the frontal lobe 

 occupies less than one half the length, and the glabellar furrows are 

 like those of Cheirurus niagarensis. The free cheeks are small, the 

 eyes opposite the ends of the second pair of furrows, and a little 

 further from the glabella than in Ch. niagarensis. The surface of the 

 cheeks shows numerous pits, while the glabella is granulose. Genal 

 spine rather long and straight. 



Only one kind of Cheirurus pygidium has been found at Waldron. 

 The spines are short and subequal in length, broad, and flat. The ribs 

 on the pleural lobes are distinctly separated by furrows, and the first 

 rib on each side has a short sharp diagonal furrow. The median un- 

 paired spine at the back is about one half as long as the ones adjacent 

 to it. 



Measurements: — The type is 35 mm. long, 52 mm. wide; the 

 glabella is 31 mm. wide at the front and 20 mm. wide at the neck-ring; 

 the frontal lobe is 17 mm. long. 



Forviaiion and locality: — Found only in the Waldron shale at 

 Waldron, Indiana. 



Cheirurus patens, sp. nov. 

 Plate 4, fig. 2. 



This species, like the previous one, is notable for the small size of 

 its cheeks. The glabella is of the insignis type, with short furrows, 

 but is rather more convex and prominent than in that species. It 

 expands rapidly toward the front, and the frontal lobe is a little longer 

 than in any other species of the genus, forming a trifle more than one 

 half the length of the glabella of the type. The outline of the frontal 

 lobe is almost exactly semicircular, and thus differs from most of the 

 other specimens seen, the ordinary outline being that of half an ellipse. 

 Since the first pair of glabellar furrows are a little further back than 

 on most species, the fixed cheeks which terminate here are shorter 

 than usual, and the eye is a little further back. 



The cheeks are full of pits, and the glabella granulose. The pos- 

 terior glabellar lobes are not strictly triangular but pentagonal, a 

 statement which is true of most species of Cheirurus, but more obvious 

 than usual in this species. 



Measurements: — Length about 31 mm., width, about 53 mm.; 

 width glabella at frontal lobe 26 mm., length frontal lobe 17 mm. 



Forviaiion and locality: — The type is a single imperfect cranidium 



