14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



The posterior cephalic margin is straight, lacking geniculation, and 

 extends into a short, outward-directed genal spine. 



Pygidium with strongly elevated axis, furrowed for entire length 

 and showing in type species nine segments ; axis almost reaching the 

 border, possessing a strong upright spine on the second ring. Pleural 

 regions strongly convex and steeply downsloping ; border furrow deep, 

 border of even width, lacking spines. Surface strongly granulate. 



Type species. — Acimetopus hilohatus Rasetti, new species. 



Occurrence. — Late Lower Cambrian of New York. 



Discussion. — The genus is characterized by the glabella deeply 

 divided into anterior and posterior lobes, a feature present in some 

 forms of Calodiscus, and also well developed in Analox. However, 

 Acimetopus is unique in the development of the extra pair of small 

 lateral lobes in the transglabellar depression. 



ACIMETOPUS BILOBATUS Rasetti, new species 

 Plate 2, figure 3 ; plate 4, figures 1-14 



Available material. — Numerous, well-preserved cephala and py- 

 gidia. The assignment of the two shields to one species is unquestion- 

 able because of the unique ornamentation among the members of 

 the faunule. 



Description. — Features indicated in the generic description are not 

 mentioned. The anterior glabellar lobe is exceedingly convex, falling 

 vertically to the preglabellar field, moderately rounded anteriorly 

 and slightly wider than the posterior lobe; the latter is more nearly 

 straight-sided. The glabellar spine varies somewhat in size and atti- 

 tude among the specimens; on the average it is directed upward at 

 an angle about 30° and is sharply pointed. The border spines are 

 situated somewhat in advance of the midpoint of the anterior glabellar 

 lobe and are short and rapidly tapered. 



The pygidial axis is deeply furrowed for the entire length, the 

 furrows being deeper laterally. The second segment has a strong, 

 long upright spine whose base somewhat encroaches on the adjacent 

 ring furrows; it was not possible in any case to extract the entire 

 spine from the matrix. The pleural regions are so convex that they 

 somewhat overhang the border furrow, which is deep and wide. 

 Border convex, relatively narrow. 



Entire surface covered with large, elevated granules of one size. 

 Length of largest cephalon, exclusive of glabellar spine, 9.5 mm, 

 width 10 mm. Length of largest pygidium 7.5 mm, width 7 mm. 



Occurrence. — Collection cs-4. North Chatham. 



