Mauylaxd Geological Survey 509 



short and sharp central spine, narrowing to the axial furrows, Ihence 

 rapidly widening to the genal spines. 



" Eyes lunate, large and elevated considerably above the summit of 

 the glabella, and closely appressed against its coalescent first and second 

 lobes. Visual surface with numerous corneal lenses, the single specimen 

 (a young individual) in which they may be enumerated, showing eighteen 

 rows, counting diagonally from the lower posterior margin, and one 

 hundred and ninety-two lenses. Palpebrum scarcely prominent; palpe- 

 bral lobe depressed and sloping abruptly to the narrow and elevated 

 palpebral furrow. Cheeks sloping abruptly from the ocular node to the 

 thickened and somewhat flattened margin. A deep sinus which, is 

 stronger in old individuals, bounds the ocular node and flattens the sub- 

 jacent portion of the cheek. 



" Thorax subrectangular, length to width as 4 to 5. Surface depressed 

 convex. Axis relatively narrow, widest at about the fifth segment, thence 

 regularly tapering to the pygidium. Pleune relatively broad, flat for 

 about one-half their width and thence rounded to the lateral margins. 

 Each segment has a slight forward curve along the axial line, being 

 sulcate on the pleurae and having the anterior limb abbreviated by the 

 beveled planes of articulation. Pygidium subtriangular, depressed convex 

 or flattened. Posterior extremity produced into a stout, upwardly curved 

 spine, usually short, but sometimes equaling the pygidium in lengih. 

 Length, including the caudal spine, equal to the width. 



" Axis having less than one-third the width of the shield on the anterior 

 extremity, regularly tapering to an obtuse, broadly rounded termination, 

 and composed of from nine to fourteen broad, flat, transverse annulations. 



" Pleurae broad and rounding more or less abruptly to the margins, bear- 

 ing eight or nine wide, flattened annulations. M'hich become obsolete just 

 within the border. Wherever the crust is retained the annulations are seen 

 to be faintly grooved near their distal extremities, but in the usual con- 

 dition of preservation as casts of the lower surface, the tendency to dupli- 

 cation is not often apparent. Doublure narrow on the sides, rapidly 

 widening toward the posterior spine, where it extends forward as far as 

 the termination of the axis. The caudal spine is not infrequently broken 



