8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28 



trated by the writer (Rasetti, 1948) and some of the ptychopariids 

 discussed herein supply ample proof. Consequently, the upper and 

 lower surfaces may differ considerably in appearance. 



Subfamily Antagminae Hupe, 1953 



A family to contain the most primitive ptychopariids was tenta- 

 tively erected by Hupe and named after the genus Antagmus. The 

 unit is here given subfamily rank since the differences between these 

 Lower Cambrian genera and Ptychoparia itself do not seem of great 

 taxonomic significance. 



It does not seem possible to assign strict diagnostic features of the 

 Antagminae, since in this difficult group of trilobites taxonomic units 

 cannot be based on morphology alone, without due regard to strati- 

 graphic and geographic factors. The most salient and commonly en- 

 countered cranidial features are described, with the understanding 

 that they are not exclusive of the genera included in the subfamily. 



The glabella is moderately tapered, always well defined at the sides, 

 in some cases almost merging in front with the preglabellar field. 

 Glabellar furrows moderately deep to obsolete ; three or four pairs 

 visible in most species ; furrows of four pairs not greatly different in 

 depth, short, straight ; first two pairs directed inward and forward, 

 last two pairs inward and backward. Occipital furrow well impressed, 

 occipital ring usually bearing a node, never spinose. Frontal area 

 usually well divided into preglabellar field and border by a marginal 

 furrow ; the latter frequently showing a median inbend due to ex- 

 pansion of the border. Palpebral area from one-half to fully as wide 

 as the glabella ; ocular ridges present ; palpebral lobes elevated, set 

 off by distinct palpebral furrows, from one-fourth to one-half as long 

 as the glabella, situated on the level of the glabellar midpoint, or 

 slightly more forward or backward. Posterior limbs on the average 

 as wide (tr.) as the occipital ring, deeply furrowed. Anterior facial 

 sutures slightly convergent to slightly divergent ; frontal portion 

 ventral-intramarginal. Surface of test almost invariably granulated. 



Most of the Antagminae are known only from cranidia. However, 

 the writer (Rasetti, 1951) described complete exoskeletons of several 

 lower Middle Cambrian species of Syspacephalus. Lochman (1952) 

 figured pygidia attributed to species of Onchocephalus. Resser 

 (1938) illustrated a complete, but poorly preserved Lower Cambrian 

 ptychopariid, "Ptychoparella" buttsi, referred by Lochman (1947) to 

 the genus Antagmus. All these observations confirm that the Antag- 

 minae have a thorax of about 15 segments, with pleura bluntly ter- 



