14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28 



type species, the upper Middle Cambrian Ptychoparella hrevicanda 

 Poulsen, but on the supposed Lower Cambrian representatives. Be- 

 sides the reasons already mentioned under the family discussion, there 

 seem other valid ones for not referring these Lower Cambrian forms 

 to Ptychoparella: (i) the position of the eyes is more posterior in 

 Ptychoparella than in Eoptychoparia; (2) the anterior facial sutures 

 are slightly convergent in Ptychoparella, slightly divergent in Eopty- 

 choparia; (3) the pygidium may have more segments in Ptycho- 

 parella, although much weight cannot be attributed to this character 

 as no pygidium can be assigned with certainty to either genus. The 

 writer carefully considered whether such forms should be assigned 

 either to Antagmus or Piasella, but the distinguishing features seem 

 worthy of generic distinction. 



Eoptychoparia differs from Antagmus in the lack of a strong rear- 

 ward expansion of the border ; from Piasella in the lesser width of 

 the palpebral area and the posterior limbs, and hence in the greater 

 relative size of the glabella compared to the fixed cheeks ; from 

 Onchocephalus in the generally more prominent, rounded glabella, 

 deeper glabellar furrows, greater convexity and horizontal position 

 of the palpebral area, and on the average more divergent course of 

 the anterior facial sutures. It is acknowledged that these differences 

 are not of great importance, and intermediate forms exist. However, 

 if lack of intermediate species were required for generic separation, 

 one would have to place most of the Ptychopariidae in a single genus. 



Besides the species described herein, the writer would refer to 

 Eoptychoparia two species described by Resser, Ptychoparella taylori 

 and P. minor, although the former, possessing greater relative widths 

 of palpebral area and posterior limbs, fonus a perfect transition to 

 Piazella. Some of Resser's species of Ptychoparella from Vermont 

 may also belong in the genus, but most of them are too poorly pre- 

 served to warrant discussion, excepting P. walcotti which seems very 

 close to the type species of Eoptychoparia. 



EOPTYCHOPARIA NORMALIS Rasetti, new species 

 Plate I, figure 2; plate 3, figures 5-1 1 



Available material. — A dozen partly fragmentary cranidia. 



Description. — Glabella prominent, fairly convex longitudinally and 

 strongly convex transversely, sHghtly tapered, rounded in front. Four 

 pairs of glabellar furrows visible on some specimens ; only third and 

 fourth pairs well impressed. Occipital ring short (sag.), bearing a 

 prominent node. Preglabellar field downsloping, as long (sag.) as 



