24 



Ampyx Halli. (N. sp.) 



Fig. 25. 

 Fig. 25.— Ampyx Halli. a, head ; b, pygidium; c, side view of the head. 



Description. — Head somewhat triangular or semioval. Glabella enlon- 

 gate oval, terminating in front with an acute elevated rostrum, the length 

 of which is not known, and truncated behind by the neck furrow, narrowly 

 convex and rather sharply carinated along the median line. Glabellar 

 furrows represented by two obscure indentations on each side, the poste- 

 rior at a httle less than one line from the neck segment, and the anterior 

 about two lines ; the latter are deep pits situated in tlie dorsal furrow or 

 just in the angle formed by the junction of the base of the glabella with 

 the fixed cheeks. The neck segment is a flat plate inclining upwards and 

 backwards at an angle of about 45°. The neck furro^v is well defined all 

 across the whole width of the head, being least distinct in passing over 

 the posterior part of the glabella. 



Pjj'gidium semioval with a flat border all round abruptly bent down at 

 nearly a right angle. Axis conical, moderately convex, extending the 

 whole length and causing a slight projection in the posterior margin. 

 Side lobes nearly flat, witli five or six flat ribs each with a fine pleural 

 groove extending the whole length. On the axis there appear to be ten 

 or twelve closely crowded annulations occupying five sixths the length, 

 the apex being apparently smooth. On approaching the margin the side 

 ribs seem to curve a little forAvards. Length of head, excluding the ros- 

 trum, 3^ lines, measured along the base of the glabella. Width of glabella 

 at neck segment 1^ line, and just in front of the anterior pits 2 lines ; ele- 

 vation at neck segment less than one line, and at front of head, so far as 

 seen, about 2 lines. These measurements refer to the largest head seen. 



No perfect head has been collected, and I cannot therefore give the 

 length of the rostrum or moveable cheeks. 



Dedicated to Dr. G. M. Hall, M.D., of Swanton, Vermont. 



Locality and Formation. — St. Dominicpie, in the County of Yamaska, 

 Canada East, and at llighgate Springs in Vermont. In the Chazy Lime- 

 stone. 



Collectors. — Dr. G. M. Hall, Rev. J. B. Perry, and J. Richardson. 



