Contributions to Palozontology. 161 



angularly bent backwards near the middle. Pygidium 

 somewhat parabolic ; the axis strong and elevated, 

 marked by several annulations, and the lateral lobes by 

 divided ribs. 



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

 movable cheeks, in one species, are strongly and pecu- 

 liarly lamellose-striate ; and in the other known species, the 

 cheek-borders are grooved, with angular strise or ridges 

 between them. 



The imperfection of the specimens is such that the generic de- 

 scription must remain incomplete, until more satisfactory material 

 can be obtained. 



PTYCHASPIS MINISCAENSIS. 



PLATE I, FIGS. 41-46; AND PLATE V, FIGS. 21 & 22. 



Dikelocephalus minixcaensis : Owen, Geological Report Wisconsin, Iowa and 

 Minnesota, page 574, Tab. 1, f. 3 & 12 ; and Tab. 1 A, f. 4 & 5. 



Head large and strong, with broad cheeks having a thick- 

 ened and striated border, which is produced in a short 

 triangular spine behind. 



Glabella large and strong, very convex, somewhat semi- 

 cylindrical, 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 furrows ; the posterior pair ex- 

 tending obliquely and deeply about one-third across the 

 glabella, and connected by a straight transverse 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 oc- 

 cupies 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 

 [Trans, v.] 21 



