60 



A COXTRIBUTIOX TO THE LO\VER DeVOXIAX FaUXAS OF MaEYLAXD 



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. Pleurae 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 

 Ijeveled planes of articulation. Pygidium sul^triangular, depressed convex 

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

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

 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. 



'• Pleura? broad and rounding more or less abruptly to the margins, bear- 

 ing eight or nine wide, flattened annulations, which 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 

 away from the margin of the doublure, giving the caudal shield a semi- 

 circular outline. 



" Surface ornamentation. The surface of the cephalon, within the 

 border and occipital ring, is covered by strong tubercles, whicli are closely 

 disposed over the cheeks and more scattered on the glabella. In old in- 

 dividuals these tubercles extend to the margin, and the orbital ridge of 

 the cheek becomes covered with fine granulations. The surface of the 

 thorax and pygidium is smooth or finely granulose. Pygidia of young 

 indi\i;luals show low nodes or tubercles upon the pleura?, apparently ar- 

 ranged in three or four oblique rows with indications of similar orna- 

 mentation upon the axis." Hall and Clarke, 1888. 



