NO. 7 PTYCHOPARIID TRILOBITES — RASETTI 25 



cranidia. Several additional cranidia were collected by the writer, 

 also from the type locality. 



Description. — Glabella fairly tapered, straight-sided, not too sharply 

 truncated in front. Three and sometimes four short, shallow glabel- 

 lar furrows visible at the sides. Occipital furrow almost straight ; 

 occipital ring expanded medially, obtusely subtriangular, bearing a 

 node. Preglabellar field somewhat shorter (sag.) than the border on 

 the outer surface, lacking a boss. Border convex, prominent, swol- 

 len medially, tapering in width at the sides on account of the straight 

 course of the marginal furrow and the curved anterior outline of the 

 cranidium. Ocular ridges wide and low on outer surface ; palpebral 

 lobes set off by a shallow^ palpebral furrow and not greatly elevated. 

 Width of palpebral area about 0.8 times width of glabella. Posterior 

 limb about as wide (tr.) as occipital ring. Surface with rather indis- 

 tinct granules. The unusually thick test of this species results in a 

 great dift'erence in the appearance of exfoliated cranidia, where the 

 glabella appears proportionately narrower and the preglabellar field 

 longer (sag.), and all furrows are accentuated. 



Remarks. — An exact comparison with the type species cannot be 

 made, since the latter is represented by distorted sandstone casts. The 

 chief difference seems to be the lack of a preglabeller boss in 

 P. zvakotti. 



Occurrence. — All the known specimens are from boulders of the 

 Ville Guay conglomerate. The figured cranidia collected by the writer 

 are from boulder O-24, Island of Orleans. Found also in boulder L-2, 

 Ville Guay. 



Types. — Holotype and paratype : U.S.N.M. No. 23529. Plesio- 

 types: U.S.N.M. No. 123879. 



PERIOMMA GASPENSIS Rasetti, new species 



Plate 4, figures 11-15 



Available nuiferial. — Eight cranidia ranging from 3 to 7 mm. in 

 length. 



Description. — Most of the characters of this species are either in- 

 cluded in the generic diagnosis or are the same as in P. walcotti. The 

 chief differences from the latter species are the somewhat shorter 

 (sag.) border, the shallowness of the median portion of the anterior 

 marginal furrow due to the presence of a preglabellar boss, and the 

 greater width (tr.) of the posterior limb, which somewhat exceeds 

 the width of the occipital ring. Surface indistinctly granulated. 



A feature observed on this species is the increased rate of tapering 



