BY R. ETHERIDGE, JUXR., AND JOHN xAHTCHKLL. 491 



smooth border is exposed bounded on outer edge by a linear 

 furrow. 



Obs. — This species in some respects resembles P. fecundus^ 

 Barr., with which we were inclined on first inspection to consider 

 it to be identical. Closer examination, however, has revealed 

 sufficient differences between them to justify us in separating it 

 from that species. 



In the first place, in our species the greatest length of the 

 glabella, including the neck ring, equals its greatest width. In 

 P.fecujidus the glabella furrows are distinct on immature indi- 

 viduals, but rarely so on mature ones, which is just the opposite 

 to the case in our species. Again, the eyes of the latter have, so 

 far as we have been able to observe in all our numerous speci- 

 mens, a constant number of seventeen vertical rows of lenses, and 

 never more than five lenses in a row, except in rare cases where 

 a rudimentary lens occurs at the top. 



The lateral extension of the neck furrow around the edge of 

 the border of the side lobes is not nearly so distinct in our species 

 as in P. fecn7idus, Barr., and it ceases in front of the eye instead 

 of joining the furrow passing round the frontal base of the 

 glabella. 



Between the thoraces of the two sjDecies there appears little 

 difference, except that the thoracic test of ours seems to have 

 been smoother, and the sides more perpendicular. 



The pygidium of our species is more nearly semicircular, and 

 its axis is not sunk between the side lobes, with an almost 

 constant number of seven segments, and rarely if ever eight. The 

 side lobes are divided into six or, doubtfully, seven pleurae. 



To sum up, our species is separated from P. fecundus by having 

 a much smaller eye, the features of Mdiich remain constant in all 

 mature individuals, a less distinct furrow separating the glabella 

 in front from the rudimentary limb, by a smaller number of 

 divisions in the axis and side lobes of the pygidium; and 

 apparently a much thinner test, which was less distinctly granu- 

 lated on the thorax and pygidium. 



