NO. 7 PTYCHOPARIID TRILOBITES — RASETTI 9 



minated, and a small pygidium, composed of very few segments, 

 which is unlikely to offer generic taxonomic characters. 



The writer would provisionally include in the Antagminae only the 

 genera based on Lower Cambrian type species, Antagmus, Aiistin- 

 villia, Crassifimbra, Onchocephalus, Periomma, Piazella, Poulsenia, 

 Proliostraciis, Somhrcrella, and Syspacephalus; also three new genera 

 described herein, Eoptychoparia, Bicella, and Luxella. Some of the 

 above-mentioned genera are known to range into the lower Middle 

 Cambrian, and it is possible that genera based on Middle Cambrian 

 type species such as Arellanella, Caborcella, and several others should 

 also be included. However, a revision of the taxonomy of the Middle 

 Cambrian ptychopariids is a task of such proportions that the writer 

 prefers, for the time being, to confine attention to classification of 

 the Lower Cambrian genera alone. For analogous reasons, genera 

 based on European, African, Australian, Asiatic, and South Ameri- 

 can forms were not taken into consideration ; however, few ptycho- 

 pariids are known from the Lower Cambrian of these areas. 



Representative species of each of the genera described in this paper 

 are illustrated by line drawings on plate i. 



Genus ANTAGMUS Resser, 1936 



Description. — Glabella of regular convexity, rounded in front, with 

 three or four pairs of furrows ; occipital furrow impressed. Frontal 

 area steeply downsloping at the sides, divided into preglabellar field 

 and border ; marginal furrow with a median inbend caused by a rear- 

 ward expansion of the border. Preglabellar field never completely 

 absent mediall3^ Palpebral area convex, on the average horizontal, 

 from 0.5 to 0.7 times the width of the glabella at its midpoint ; ocular 

 ridges well marked ; palpebral lobes one-third to one- fourth as long 

 as the glabella, situated slightly back of the glabellar midpoint. Pos- 

 terior limbs as wide (tr.) as or a little wider than the occipital ring: 

 distal portion as wide as or somewhat narrower than the proximal por- 

 tion ; marginal furrow deep, reaching the distal end of the limb. An- 

 terior facial sutures divergent at least for some distance in front of 

 the eyes, convex outward ; frontal portion marginal or slightly ven- 

 tral for a considerable distance. Posterior branch directed rather 

 definitely outv/ard behind the eye, curving backward near the posterior 

 margin. Surface of test usually with fine granules. 



Type species. — Antagmus typicalis Resser. 



Remarks. — The above description was based chiefly on Antagmus 

 gigas, a species here described which seems extremely close to or 

 possibly identical with the poorly represented type species. 



