October, 1913. New Trilobites — Slocom 51 



produced into a long acuminate process pointing obliquely upward. 

 Dorsal furrows visible only in the occipital region. Glabella not 

 defined laterally or anteriorly, depressed convex, greater elevation at 

 its posterior margin, which is the greatest elevation of the entire test. 

 Fixed cheeks not defined. Free cheeks large, widest near the eyes, 

 where they slope abruptly to the lateral margins; the genal angles are 

 produced into short spines, extending directly backward as far as the 

 sixth thoracic segment ; the anterior portions narrow gradually forward 

 until they meet at the anterior margin. The facial sutures originate on 

 the posterior margin of the cephalon about midway between the dorsal 

 furrows and the genal angles, converging slightly to the eyes; in front of 

 the eyes they converge more rapidly, extending subparallel to the 

 antero-lateral margins of the* cephalon and meeting in front of the 

 glabella. The palpebral lobes are prominent, their proximal edges 

 being produced towards the median line of the glabella and interrupting 

 the dorsal furrows; the transverse ridges thus formed appear to be 

 comparable to lateral glabella lobes rather than ocular ridges. Form 

 of the eyes not known, but one of the palpebral lobes on a cranidium 

 (Mus. No. P 16998) indicates that they were elevated similar to those 

 of Nileus vigilans. Occipital segment and furrow obsolete. Shallow 

 posterior cheek furrows extend laterally from the dorsal furrows, meet- 

 ing the lateral furrows near the genal angles. 



Thorax composed of eight segments. Dorsal furrows shallow; axis 

 depressed convex, slightly tapering posteriorly; occupying somewhat 

 more than one-third the width of the thorax; no transverse furrows; 

 the pleurae curve outward and then abruptly downward to the lateral 

 margins; distal extremities rounded; angular furrows originate at the 

 dorsal furrows and cross the pleurae diagonally. 



Pygidium slightly narrower and much shorter than the cephalon, 

 marginal border denned only near the posterior margin: Axis tapering 

 to a prominent rounded termination well within the margin. The 

 pleural lobes curve abruptly to the lateral margins. The segmentation 

 of the pygidium is not visible on the outer surface of the test, but on its 

 inner surface some traces may be found on both axis and pleura 1 . 



The measurements of the type specimen are as follows: Length 

 over all 89. 1 mm. ; width at genal angles 37.2 mm. ; length of the cephalon 

 on median line 42.5 mm.; length of cephalon including genal angles 57 

 mm.; length of thorax 21.3 mm.; width of thorax at anterior segment 

 33 mm.; length of pygidium 26.5 mm.; width of pygidium at anterior 

 margin 29.5 mm. 



So far as known to the writer, only two American species have been 

 referred to this genus. These are M. ? gonioceras Meek from the 



