S«4 PALEONTOLOGY OF NEW-YORK. 



Eyes of medium size, their summit less elevated than the glabella, ex" 

 tending backwards to the line of the occipital furrow, composed of 

 seventeen vertical ranges of lenses ; the entire number of lenses in 

 full-grown specimens about one hundred, and varying in the specimens 

 examined from ninety-three to one hundred and three. 



The axis of the thorax is prominent, and narrower than each of the 

 lateral lobes; the annulations furnished with a prominent node at each 

 extremity. The lateral lobes are flat or somewhat concave towards the 

 axis, the articulations bending abruptly downward from the middle to- 

 V ards the extremities ; each articulation strongly grooved, the groove 

 extending beyond the curvature. 



Pygidium semicircular ; the axis prominent, with about nine annulations ; 

 the lateral lobes having about five or six ribs, each with a groove 

 along the centre. 



SuKFACE of the glabella pustulose, and of the articulations granulose, with 

 some larger granules or pustules. The crust is thin, and the interior 

 of the glabella shows distinct cavities corresponding to the external 

 pustules. Hypostoma broad hastate ; the buccal extremity obtuse, with 

 a minute central point. 



This species, after the Dalmanites pleuroptyx, is more common than any other 

 trilobite in this group of strata. It is not unfrequently enrolled, though nearly all 

 the specimens in this condition are imperfect. The separate heads, which best illu- 

 strate the characters of this portion of the animal, are from the decomposed shaly 

 limestone. 



This species resembles the Phacops fecundtis of Bakrande ; but the eyes are 

 smaller, with a less number of lenses, while the head is proi)ortionally less broad, 

 and there are fewer ribs in the lateral lobes of the pygidinm. It difl'ers from the 

 P. hufo in the transverse furrows of the glabella, which in that one are rarely de- 

 fined; in the characters of the eye; and in the prominence of the tubercles at the 

 extremity of the annulations of the axis, as well as in the ribs of the pygidium, 

 which are more bent backwards in this one. The crust of the thorax in the P. bufo 

 is more finely granulate, and the axis less prominent. 



Fig. 15. An entire specimen wliich has the head compressed from above, and the eyes a little 

 distorted.- 



Fig. 16. View of a specimen whioh is enrolled. 



