NO. 4 CAMBRIAN TRILOIUIES, 2D CONTRIBUTION RESSER 3 



This is a rather small form characterized by long, slender pleural 

 and pygidial spines, with a macropleural development of the last 

 thoracic segment. 



Occurrence same as preceding. 



Holotype. — U.S.N.M. no. 63766; paratypes, nos. 53402, 53404, 

 53405, 53406, 63764, 63765. 



Albertella robsonensis, n. sp. 



Albertella bosworthi Walcott (part), Smithsonian Misc. Coll., vol. 67, no. 2, 

 p. 38, pi. 7, figs. 2-2b, 1917 (see A. bosz<.'urthi). 



The glabella is long and somewhat more expanded than in the more 

 southern species. The pygidium reflects the same characteristic in its 

 narrowness and long, narrow, prominent axis. Its pleural lobes are 

 very flat, even when compared with A. similaris. 



Middle Cambrian, Chetang; (loc. 6ip) Coleman Creek, and (loc. 

 6iw) Terrace Creek, Robson Park, Alberta. 



Cotypes. — U.S.N.M. nos. 63759-63761. 



AMECEPHALINA Poulsen, 1927 



Amecephalina convexa (Walcott) 



Anomocare convexa Walcott, Smithsonian Misc. Coll., vol. 75, no. 4, p. 87, 

 pi. 17, figs. 2-2d, 1911; Research in China, vol. 3, Carnegie Inst. Publ. 54, 

 p. 187, pi. 18, figs. 3-3C, 1913. 



Middle Cambrian, Conasauga ; (loc. 90X) 3 miles east of Center, 

 Alabama. 



Lectotypc.^U.S.'NM. no 57597 ; paratypes, nos. 57595, 57596. 



ANTAGMUS, n. gen. 



For many years certain common Lower Cambrian trilobites were 

 referred to various genera, depending on the genus to which the 

 author was comparing them at the moment, or on a particular feature 

 which attracted his attention. Some revision is now possible, but 

 until this genus and its related forms can be studied thoroughly, any 

 suggested realignment of the species must be tentative. 



Diagnosis. — Cranidium rather wide and convex in both directions ; 

 facial suture diverging anterior to the eyes. Glabella well defined, 

 tapering, about two-thirds the length of the cranidium, with two or 

 three pairs of short glabellar furrows. Brim consists almost entirely 

 of a rim, usually somewhat thickened and particularly characterized 

 by its increased width in the middle, which is due to the backward 

 course of the anterior furrow to meet the dorsal furrow in front of the 

 cranidium. 



