CONTRIBUTIONS TO PALiEONTOLOGY. 171 



The surface of the front of the glabella, the fixed and movable 

 cheeks, in one species, are strongly and peculiarly lainellose- 

 striate ; and in the other known species, tho cheek-borders are 

 grooved, with angular strise or ridges between them. 



The imperfection of the specimens is such that the generic description 

 must remain incomplete, until more satisfactory material can be obtained. 



PTYCHASPIS MINISCAENSIS. 



PLATE VI, FIGS. 41-46; AND PLATE X, FIGS. 21 & 22. 



Dikelocephalus minis caensis ; Owen, Geol. Report Wisconsin, Iowa and Minnesota, pago 



574, Tab. 1, f . 3 & 12;2:and Tab 1 A, f. 4 & 5. 



Head large and strong, with broad cheeks having a thickened and 

 striated border, which is produced in a short triangular spine 

 behind. 



Glabella large and strong, very convex, somewhat semic3-lindri- 

 cal, about three- fourths as wide as long, the width at the 

 anterior end about one -fifth less than the width at its base, 

 rounded or subtruncate anteriorly, marked by two pairs of fur- 

 rows ; the posterior pair extending obliquely and deeply about 

 one-third across the glabella, and connected by a straight trans- 

 verse furrow. The second pair of furrows are shallow, oblique, 

 and in older specimens can be traced about one-third across the 

 glabella. In older specimens the anterior lobe occupies about 

 one-half the length of the glabella, while in younger ones it is 

 scarcely more than one-third the length. The occipital furrow 

 is strongly defined ; the occipital ring strong and prominent, 

 and of nearly equal width throughout. Dorsal furrow strongly 

 defined, and continued in froht of the glabella. 



Fixed cheeks comparatively wide. 



Facial suture vertical from the contour line in front to the inside 

 of the palpebral lobe ; thence turning a little outwards, it comes 

 to the posterior margin halfway between the dorsal furrow and 

 the outer margin of the movable cheek. The frontal limb is 

 somewhat abruptly convex from the furrow, but never rises 

 nearly so high as the frontal lobe of the glabella, and is ab- 

 ruptly bent downwards to the anterior margin. Eyes unknown. 



Movable cheek large, somewhat trapezoidal : the outer limb is 

 extremely thickened, with a few eoarse longitudinal striae pre- 

 served in the cast, extended behind, and uniting with the 

 thickened posterior border, it forms a spine three-fourths as 

 long as the body of the cheek. Within the thickened border 

 there is a distinct groove, which is not quite united with the 

 groove of the posterior limb. 



