2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 



plete bibliographies are given, but they include references to all papers 

 that add information. Care has been exercised to conform strictly 

 to the rules of the International Commission on Zoological Nomen- 

 clature. For the sake of lowering publication cost illustrations are 

 omitted from this article, even though they would be desirable, par- 

 ticularly since most papers describing Cambrian fossils are now out of 

 print. New genera and species which require illustration to conform 

 to the rules will be placed in a separate series of papers. Few foreign 

 species are given consideration because several reports either in press 

 or about to be printed care for many of them. 



ACROCEPHALITES Wallerius, 1895 



Acrocephalites Wallerius, Unders zonen med Agnostiis Icavigatns i Vestergot- 



land, Sweden, p. 52, 1895. 

 Acrocephalites Walcott, Smithsonian Misc. Coll., vol. 64, no. 3, p. 174, 1916. 



Much confusion exists respecting this genus, as many different 

 trilobites have been referred to it simply because they possess a 

 median boss. In fact, the genus was not understood until Wester- 

 gaard ^ published photographs of the type species. From his studies it 

 is evident that the North American forms cannot even belong to the 

 same family, and consequently fall into other genera. Restricting the 

 genus to species congeneric with the genotype, only three very rare 

 forms remain, viz., Acrocephalites stenotnetopus (Angelin) and A. ? 

 rams Westergaard, from Sweden, and A. vigilans Walcott and Resser 

 from Novaya Zemlya. 



Diagnosis. — Cranidium alone known. A'iewed vertically the facial 

 suture converges forward from the posterior margin, but in side view 

 it rises sharply from the basal plane of the head to the eyes and then 

 drops ofif equally rapidly to the anterior angles. Cranidium keeled. 



Glabella large, about two-thirds as long as the head, tapering for- 

 ward, but truncated anteriorly ; two pairs of glabellar furrows turn 

 sharply back ; occipital furrow and ring well defined ; sharp occipital 

 spine. Brim with a well-defined rim about one-third the width of the 

 preglabellar area ; rim thickened and extended forward into a blunt 

 spine medially. Fixed cheeks half as wide as the glabella ; palpebral 

 lobes strongly curved, elevated, and entirely beyond the rather straight 

 course of the facial suture. Surface granulose. 



Genotype. — Solenopleuraf sfenomefopa Angelin. ^ 



Range. — The genus is confined to Upper Cambrian strata in the 

 Atlantic Province. 



* Sveriges Geol. Unders., ser. Ca, no. 18, p. 123, pi. i, figs. 20, 21, 1922. 



