46 Traits. Acad. Sci. of St. Louis. 



Emmons in being regiilaiiy ovate, fifty millimeters long 

 b}^ seventy-five millimeters broad, and in the surface be- 

 ing plain on either side of the median fold. The speci- 

 men figured by Emmons seems to have been deformed by 

 pressure applied from the sides. 



HYOLITHES^ n. Sp. 



This form differs from H. haconi Whitfield in the ven- 

 tral surface being evenly convex instead of subangular. 



The specimens in the collection are too fragmentary 

 for description. Number 11532 of the invertebrate pal- 

 eontological collection of Walker Museum. 



PTEKYGOMETROPUS LINCOLNENSIS, n. Sp. 



PI. vii. /. 17-19. 



General form elongate, slender, tapering gradually 

 posteriorly. Cephalon subcresentiform, with a com- 

 pressed, obtusely angular projection in front. Frontal 

 lobe of glabella short and broad, proportion of length to 

 breadth about six to seven. First lateral furrows reach- 

 ing the dorsal furrows and separating the first lateral 

 lobes from the frontal lobe. Inner ends of these furrows 

 about two millimeters apart. Second lateral furrows 

 very short and deeply impressed at their inner ends. 

 First and second lateral lobes confluent at their outer 

 ends. Third lobe of glabella very small and not confluent 

 with the second lobe. Occipital ring prominent at the 

 median line, projecting above the rest of the cephalon. 

 It bears no tubercle. Frontal lobe and sometimes the 

 first and second lateral lobes sparsely tuberculate. Eye 

 elongate, reaching from the outer end of the first lateral 

 furrow to the occipital furrow. Posterior part of fixed 

 cheek very small and usually not preserved with the spec- 

 imens. It bears no genal spine. 



Thoracic segments eleven. Pygidium subtriangular. 

 Pleura with eleven or twelve segments, one or two of the 

 posterior ones indistinct; axis tapering gradually be- 

 hind and reaching nearly to the posterior end of the 



