38 BULLETIN OF THE 



long has a process of the usual type, namely, a small mucronate tubercle or 

 spine at the posterior extremity. The species occasionally attains a length of 

 head of 20 mm. The average size is within 10 mm. Anterior to the glabella 

 is a groove which separates the anterior border of the head from the glabella 

 and the ocular ridges. Within the border is a broad, shallow groove. It is 

 of medium size, rounded and curved. The distance between the extremities 

 of the border, at the facial suture, is slightly less than the distance between 

 the grooves defining the palpebral lobes. In line with the anterior margin 

 of the glabella, or slightly behind the same and parallel with the anterior 

 border, are the ocular ridges, increasing in prominence with the size of the 

 individual, joining laterally the anterior end of the palpebral lobe. The 

 groove which more or less distinctly defines the posterior margin of the ocular 

 ridge joins the more distinct groove which separates the palpebral lobe from 

 the fixed cheeks. The palpebral lobes are obliquely curved, having a postero- 

 lateral direction. The facial sutures anterior to the palpebral lobes bend 

 slightly outwards to meet the anterior margin of the head. Posteriorly they 

 curve towards the side and backwards, cutting the posterior edge within the 

 postero-lateral angles. The cheeks are more convex in young specimens; in 

 larger individuals they are only moderately curved. The extension of the 

 occipital groove over the sides of the head is quite deep and distinct. Numer- 

 ous specimens of free cheeks show that the postero-lateral extremities of the 

 head were quite strongly spined. 



Three specimens have been found preserving most of the segments of the 

 thorax, the posterior ones being more or less injured. One of these specimens 

 shows thirteen segments, but there may have been fourteen or fifteen in the 

 complete individual. The pygidium, judging from the specimens at hand, 

 must have been relatively very small, perhaps about the size of that of 

 Ptychoparia Piochensis. The pygidium has not been found. 



The side lobes of the thorax are moderately broader than the axial lobe. 

 The middle lobe is strongly convex, and marked with a median row of mu- 

 cronate tubercles, or small spines. These in the individual best preserving 

 them were more prominent along the middle segments, being of moderate size 

 anteriorly and practically obsolete in the last three or four segments. The 

 species, as already noted, is quite variable; but the variations are none of them 

 of any marked character, and all are abundantly connected by intermediate 

 specimens. It takes the place of the series of species from the Vermont sec- 

 tions known as Ptychoparia Adamsi, P. Teur.er, P. Vulcanus, and the type of 

 fossils in which the border is separated only by a short interval from the gla- 

 bella, as figured by Walcott under P. Adamsi (Bulletin U. S. Geol. Survey, 

 No. 30, PI. XXVI. fig. 1 c). These specimens would have been placed under 

 P. trilineata, Emmons, had not such a good observer as Walcott decided, 

 from a personal observation of the types, that the species was properly a 

 Conocoryphe, which our specimens decidedly are not. 



Locality and position. — Stations Nos. 2 and 3, North Attleborough, Mass., 

 Cambrian, 300 specimens. 



