NO. 7 PTYCHOPARIID TRILOBITES — RASETTI 1 7 



tarius Lochman and Proliostracus goodzmni Resser. Lochman ex- 

 cluded the latter species from Onchocephalus on the basis of the 

 slightly lesser width of the palpebral area, a character which the writer 

 does not consider of generic importance. 



One new species and several unnamed forms are described herein. 



ONCHOCEPHALUS SULCATUS Rasetti, new species 

 Plate I, figure 3; plate 3, figures 16-19 



Available material. — Two well-preserved cranidia. 



Description. — Glabella of moderate elevation, straight-sided, fairly 

 truncated in front ; dorsal furrow fairly deep at the sides, shallow an- 

 teriorly. Four pairs of glabellar furrows visible, but only third and 

 fourth pairs moderately well impressed. Occipital ring bearing a node. 

 Preglabellar field shorter (sag.) than border medially. Border 

 strongly convex, elevated, expanded medially, causing a slight median 

 inbend of the marginal furrow. Palpebral area convex, on the aver- 

 age almost horizontal, 0.7 times as wide as the glabella. Palpebral 

 lobes strongly elevated, 0.4 times as long as the glabella; distance 

 from posterior end of palpebral lobe to posterior margin about equal 

 to length of palpebral lobe. Posterior limbs as wide (tr.) as occipital 

 ring; distal portion appreciably narrower (tr.) than proximal por- 

 tion. Anterior facial sutures parellel for a short distance in front of 

 the eyes, appreciably convergent at the level of the marginal furrow ; 

 posterior branch reaching margin with a wide curve. Length of 

 holotype cranidium 6 mm. Surface finely granulated. 



Remarks. — The species is typical of Onchocephalus and closely re- 

 sembles 0. buelnaensis Lochman and 0. mexicanus Lochman, differ- 

 ing mainly in the greater prominence of the anterior border and con- 

 vexity of the palpebral area. 



Occurrence. — Boulder G-41, Grosses Roches. 



Ty/)^.?.— Holotype : U.S.N.M. No. 123869. Paratype: U.S.N.M. 

 No. 123870. 



ONCHOCEPHALUS, species undetermined No. i 



Plate 3, figure 20 



Available material. — One cranidium. 



Description. — This form is characterized by an almost unfurrowed 

 glabella with slightly concave side outline. Preglabellar field half as 

 long (sag.) as border on median line. Border very convex, not ap- 

 preciably expanded backward medially. Palpebral area slightly con- 



