98 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



times as long as glabella plus occipital ring, set off by shallow but 

 distinct furrow even on outer surface ; its anterior end almost at the 

 level of the front of the glabella, its posterior end slightly anterior to 

 level of glabellar midpoint. Distance to posterior margin about twice 

 length of palpebral lobe. Anterior section of facial suture straight to 

 border furrow, divergent as the average in Aphelaspis ; posterior sec- 

 tion directed straight outward and backward, curving rather sharply 

 backward before cutting posterior margin at right angle, defining much 

 longer (exsag.) and narrower (tr.) posterior area than in Aphelaspis 

 species ; width of posterior area less than width of occipital ring. 



Free cheek proportionately wide, evidently steeply sloping. Ocular 

 platform convex near the eye. Border furrow shallow and broad; 

 border narrow, convex as in cranidium. Facial suture cutting margin 

 at considerable distance from short, slender genal spine. The pygidium 

 has not been identified. 



Length of largest among hundreds of cranidia observed 5.5 mm. 



Discussion. — It was mentioned in the generic description that Para- 

 phelaspis resembles immature individuals of Aphelaspis in several 

 respects. This also agrees with the fact, apparent from the description 

 and the illustrations, that the similarity to Aphelaspis increases with 

 increasing size of the cranidia of Par aphelaspis, especially in the fea- 

 tures of greater relative length of the frontal area and width of the 

 palpebral area. Nevertheless, there are still considerable differences 

 between the largest cranidia of Paraphelaspis vigilans and individuals 

 of the same size of all the known species of Aphelaspis. In particular, 

 immature cranidia of the two species of Aphelaspis that occur in asso- 

 ciation with Paraphelaspis are known and are quite different from 

 Paraphelaspis. Of all species of Aphelaspis, A. inermis is possibly 

 closest to Paraphelaspis. 



Occurrence. — The type locality is cns/20, Washburn. Also present 

 in collections cns/20a, Washburn, cnr/4. Lost Creek, ens VI 5, cns'V 

 15, Three Springs, and U.S.G.S. 2970. The species has been found 

 only in association with Aphelaspidella macropyge. 



Types.— Holotype: U.S.N.M. 144683. Paratypes: U.S.N.M. 

 144684-5. 



Genus DYTREMACEPHALUS Palmer, 1954 



Type species. — Dytremacephalus granulosus Palmer. 



DYTREMACEPHALUS ANGULATUS Rasetti, new species 



Plate 21, figures 1-9 



Available material. — Large numbers of cranidia, a few free cheeks 

 and pygidia in excellent state of preservation. 



Description. — Glabella tapered, straight-sided, truncate in front, of 

 moderate convexity, defined by deep axial furrows at the sides, a 



