552 bulletin: museum of comparative zoology. 



oblong, sides parallel, obtusely rounded in front, neck-segment elevated 

 at the posterior margin; neck-furrow in its middle-third parallel with 

 the posterior margin; at each end for one third the length sloping 

 backward; the posterior lobe of the glabella transversely oval, com- 

 pletely isolated; the median furrows lying nearly in a line across the 

 glabella at midlength, nearly straight, and each in length about one 

 third the width of the glabella; the anterior pair at a little more than 

 one fourth the length from the front, curved slightly backward and 

 inward. Thorax nearly twice the length of the glabella; the axis less 

 than one third the whole width, gently tapering backward ; the pleural 

 groove short, in length about one half the width of the axis, crossing 

 the pleura obliquely outward and downward at an angle of about 45°; 

 pygidium about half the length of the glabella, composed of three 

 articulations, the backward curving extremities of which form six 

 short obtuse points. 



A comparison of figure 7, a reproduction of the type of C. meekanus, 

 with this description of Ch. icarus Billings, will serve to show the 

 identity of the Richmond form with Billings's species. This descrip- 

 tion, both in the abridged form just given and in its entirety, are in 

 perfect accord with C. meekanus Miller, and might well have been 

 written of it. As only a few specimens are known of either form, the 

 supposed difference in size, cited by Miller, would not seem to be 

 sufficient to constitute a specific distinction. The supposed difference 

 in horizon which Miller cites is now known not to exist. For these 

 reasons it seems best to consider C. meekanus Miller as a synonym of 

 Ch. icarus Billings. 



Ch. icarus Billings is not placed under Ceraurus on account of the 

 smoothness of the glabella and of the subequality of the pygidial spines. 

 It is not placed under Cheirurus on account of the course of the poste- 

 rior pair of glabellar furrows, and is, therefore, referred to Ceraurinus. 



Ceraurinus trentonensis, sp. nov. 



Plate, fig. 5-6. 



Glabella of medium size, two thirds as wide as long, expanding 

 slightly forward, the three posterior glabellar lobes of about equal size, 

 the frontal lobe larger and forming about one third of the glabella. 

 The two anterior pairs of glabellar furrows are sharply incised, but 

 are not broad; they curve inward and gently backward till about 



