;i PALEONTOLOGY OF NEW YORK. 



species known to us from this formation in Ohio, to which such fragments 

 could be referred, and none in the Corniferous limestone of New York, 

 except I), myrmecophorus, in which species the cephalon was undoubtedly 

 similar in many respects to that of D. Helena, though of much larger dimen- 

 sions than are indicated by these fragments. It seems necessary to establish 

 Mr. Conrad's specific name, aspedans, upon a basis which will include the 

 forms heretofore referred to D. Helena and D. Ohioensis. 



Tin' description of the original fragment is as follows: " A small portion 

 of the buckler and one eye only is visible, but the eye is of an extraordinary 

 height, the margins parallel, and the lenses arranged in parallel longitudinal 

 lines, small and very numerous." 



In this specimen the eye is remarkably elevated, sub-semi-cylindrical, 

 reaching a height of 9 mm., with a width of 8 mm. across the base. The 

 corneal lenses are numerous, and though the condition of preservation does 

 not permit the enumeration of them, thirty rows are visible, some of them 

 containing as many as thirty-four lenses each. It would therefore be safe to 

 infer that the eye bore not less than 700 lenses. The attached portion of 

 the cheek has a broad flattened border, and is covered with strong, closely 

 crowded tubercles. 



Additional details of the Cephalon are furnished by the Ohio specimen, as 

 follows: the outline of the shield is semi-elliptical, the broad flat border 

 slightly thickened toward its inner margin, the marginal sulcus deep and 

 moderately broad, the genal angles produced into long sharp spines; the 

 facial suture takes its origin at a point about half-way from the apex of the 

 cheek-spine to the anterior extremity, passing abruptly forward over one- 

 hall' the width of the border, thence straight across to the marginal sulcus, 

 and inward to the inner angle of the visual surface; over the convex surface 

 of the cheek it lies in a deep groove; the surface of the cheek beneath the 

 e\ e is slightly flattened and the orbital ridge is well defined ; occipital furrow 

 and ring moderately strong. 



Of the thorax nothing has been observed. 



