(vi) 70 Paheontologia ,Sm'>a. S^r. B. 



Still more mai-ked tliaii the preceding ones and with the same oldiqueness at their ends, 

 are continuous. Th(> second and third lateral furrows as well as the occipital fmTOw, are 

 separated by almost equal intervals. The occipital ring, in the same relief as the glabella, 

 is large, with curved arc section, its width is greater in the middle than at the ends; on 

 its posterior margin is inserted a strong occipital spine of which only the base, having 

 the appearance of a large tubercle, is visible. The fixed cheeks, incomplete in all our 

 specimens, are narrow and show a convexity almost as marked as that of the glabella; 

 The rim which bounds them posteriorly is smaller than the occipital ring. Ocular lobes 

 small, raised in the vertical plane and almost parallel to the dorsal furrows of the glabella. 

 The width and the convexity of the frontal liml) are almost equal to the width and 

 conv(>xity of the fixed cheeks; Its surface blends laterally and Ixackwards in the surface 

 of the fixed cheeks, in such a Avay that the glabella is surrounded by a perfect rectangular 

 frame, which gives to the cranidium of our species a very individual appearance. The 

 v/hole surface is covered liy little tubercles, either subcircular or elliptical, drawn close 

 together and sometimes mingling and scattered without symmetry. 



"The free cheeks, the thoracic fragments and the separated pygidia which 

 accompany the heads described above, are simply mentioned here, with all reservations 

 as to their belonging to one or the other of the two varieties of Pt. valcotti. The free 

 cheeks are large, one of the specimens is a little smaller than the others and this 

 peculiarity allo^vs us to suppose that it belongs to the long and narrow variety rather than 

 to the short variety of Pt. walcotti, the glabella of this one being much larger than that of 

 the long variety. The genal angles are not raised, they are situated in the prolongation 

 of the posterior edge of the head. The genal spine is not very long but wide and robust, 

 very diverging. It makes way without any deviation to the marginal rim. The thoracic 

 fragments observed on the same fragments of shale, are much mutilated, with furrowed 

 pleuraj and rounded arched axis. No other characteristic is noticeable. 



"AH the pygidia are of the same type and identical, cne with the other. They 

 are particularly remarkable because of their very transverse form and the strong inflection 

 of the upper edge. The entire marginal region of these pygidia are thrown backwards 

 and form a very obtuse angle sometimes even, in certain specimens, showing a rectilinear 

 trace (perhaps as the result of a slight deformation). The rachis, with semicircular 

 section, truncato-conical, is composed of five large segments, rounded and separated by 

 deep furrows. The posterior segment, larger than the preceding ones, joins the 

 posterior edge by an abrupt inflexion. On the lateral lobes can only bo distinguished 

 the proximal end of two upper segments, the following ones being entirely erased- the 



