October, 1913. New Trilobites — Slocom • 81 



A small coiled specimen (PI. XVIII, figs. 4-5) in the collection of 

 Mr. A. G. Becker, found associated with typical specimens, is doubt- 

 fully referred to this species. It differs from the type in having a 

 smooth instead of a pustulose glabella and the pygidium appears to be 

 shorter in proportion to its width. Considering these characters in 

 connection with its small size, it is probable that they only indicate the 

 immaturity of the specimen. Its dimensions are: Length of cephalon 

 5 mm.; length of thorax 10.4 mm., length of pygidium 3.3 mm.; width 

 at genal angles 6.8 mm.; width at anterior margin of pygidium 4.9 mm. 



P. fredricki is distinguished from P. larrabeei by having five rows of 

 eye facets instead of eight, by its more inflated anterior portion of the 

 glabella, by its thicker and shorter anterior margin, by its shorter 

 pygidium and fewer annulations on its axis, and by the anterior limbs 

 of the facial suture being less divergent. So far as is known to the 

 writer, the number of rows of eye facets has not previously been used as 

 a specific character, but it seems to be a constant character in the thirty 

 specimens of the two species which he has observed. Specimens of 

 P. callicephalus from the Trenton of Ottawa, Canada, which appear 

 to be typical, have eight rows of eye facets. P. fredricki appears to be 

 related to P. callicephalus, but aside from the eye facets, the glabella is 

 more inflated anteriorly and the anterior margin is smaller and less 

 angular in P. fredricki. 



The specific name is given in honor of Dr. Fredrick Becker, who was 

 one of the first collectors of fossils in Fayette County and who gave the 

 writer much valuable information as to localities. 



Localities and horizon. — The type is from the top of the Lower 

 Maquoketa beds at Bloomfield, Iowa. The species has been observed 

 in beds somewhat lower down at Clermont and at Postville Junction, 

 Iowa. 



Pterygometopus larrabeei sp. nov. Plate XVIII, Figs. 6-8. 



Type specimen No. P 11 256 Field Museum. 



Cephalon sublunate in outline, anterior margin produced into a thin 

 subangular lip, genal angles well back of the occipital ring, rounded. 

 Glabella large, depressed, convex, about twice as wide in front as at 

 the occipital ring, anterior lobe transversely elliptical sloping gently 

 towards the front, comprising fully half the glabella; anterior pair of 

 glabella furrows originating at the anterior angles of the eyes and pass- 

 ing obliquely backward but not meeting at the median line of the gla- 

 bella; second pair of glabella furrows shorter and shallower than the 

 first, directed obliquely forward; third pair of glabella furrows directed 

 towards the axis of the glabella for a short distance, then bifurcating, 



