LOWER HELDERBERG ROCKS. 335 



Fig. 17. The head of a larger individual which fho-vs the transverse furrows, and preserves 

 the eyes in their proper form. 



Fig. 18. A larger head, which has few pustules in the space between the eye and the dorsal 



furrow. 

 Fig. 19. Frontal view of fig. 17. 

 Fig. 20. Profile of the same. 



Fig. 21. View of the lower side of the head of another specimen, showing some crenulations 

 along the marginal furrow. 



Fig. 22. The lower side of another specimen in which the granulation is worn from the 



surface of the glabella, and showing the line of the hypostomal suture. 

 Fig. 23. The eye enlarged. 



Fig. 24. A portion of the eye, from which the lenses have been removed by weathering. 

 Fig. 25. The hypostoma. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Helderberg moutains, Catskill, Becraft's mountain, Schoharie, Carlisle, 

 Cherryvalley, and other places. 



Pliacops liudsonicus ( n. s.). 



Plate LXXIIL Fia. 26, 27, 28. 



Head semielliptical, the length greater than half the width ; the posterior 

 angles scarcely extended, and slightly rounded. 



Glabella subpentagonal ; length nearly one-third greater than the width. 

 Frontal lobe very prominent, gibbous above : middle and anterior 

 transverse furrows distinctly impressed in the cast j first annular fur- 

 row faintly defined ; first annulation not prominent, with two pustules 

 at the summit and a node at each extremity : occipital furrow and 

 annulation strongly defined. Cheeks triangular, not produced behind. 



Eyes small, extending backwards to the line of the first annular furrow, 

 having an elevation of four ranges of lenses. 



This species is founded on a single head ( the test being removed from the gla- 

 bella), which is more produced in front than the P. logani : the eyes are smaller, 

 and not extending so far backwards. 



Fig. 26. The head of this specie^. 

 Fig. 27. Profile of the same. 

 Fig. 28. The eye enlarged. 



Geological position and locality. In the compact beds of the shaly limestone : 

 Becraft's mountain, near Hudson. 



