NO. 5 UPPER CAMBRIAN TRILOBITES RESSER 25 



IRVINGELLA TUMIFRONS (Hall and Whitfield) 



Plate 4, Figures 42, 43 



Chariacephalus tumifrons Hall and Whitfield, U. S. Geol. Expl. 40th Par., 



vol. 4, p. 224, pi. 2, figs. 38, 39, 1877. 

 IrvingcUa tumifrons Resser, Smithsonian Misc. Coll., vol. 97, No. 10, p. 33, 1938. 

 Irvingella {Irvingellina) tumifrons Kobayashi, Jap. Journ. Geol. Geogr., vol. 



IS, Nos. 3-4, p. 17s, 1938. 



The present study has led to the conclusion that this species belongs 

 in Irvingella. Several additional cranidia, distorted in other directions 

 than in the holotype, allow a reconstruction. It will be observed in 

 figure 43 that on the left side of the specimen, as mounted, an anterior 

 furrow seems to separate a rim and preglabellar area, but on the other 

 side none appear \ From the fact that other specimens also fail to 

 show an anterior furrow, we may conclude that this seeming furrow 

 is merely the result of compression. It is, of course, possible that all 

 species of both Irvingella and of ChariocepJialus, if they have a fairly 

 wide anterior angle, may possess an incipient anterior furrow. 



Secret Canyon shale ; Pogonip Mountain, White Pine District, 

 Nevada. 



Holotype.— {J. S.I^M. No. 24561. 



PARAIRVINGELLA Kobayashi, 1938 



Parairvingella Kobayashi, Jap. Journ. Geol. Geogr., vol. 15, Nos. 3-4, p. 175, 

 1938."^ 



Kobayashi erected Parairvingella as a subgenus, based on the 

 Nevada specimen which Walcott erroneously identified as Chario- 

 cephahis tumifrons Hall and Whitfield, renaming it Irvingella 

 {Parairvingella) angustilimhatiis. Long ago I recognized the distinct- 

 ness of this specimen, not only specifically, but generically, and so 

 labeled it. Kobayashi extracted his data from my partially completed 

 notes. Even though there is no striking difiference between Parair- 

 vingella and related genera, there seems to be sufficient difference to 

 raise it to full generic rank. I have referred Irvingella arctica Walcott 

 and Resser from Novaya Zemlya to the same genus as Walcott's 

 Nevada specimen, although some doubt of its true generic affinity still 

 remains. At the same time three new species are recognized among 

 the Nevada material. 



Parairvingella has the glabellar and eye structure like Irvingella, 

 and a brim consisting of a narrow preglabellar area and rim. The 

 distinctive feature is the preglabellar area in which we find a transi- 



