3«l PALiEONTOLOGY OF NEW-YORK. 



either of the preceding species except D. tridens, and may usually be distinguished, 

 particularly on the border or limb, by its coarser pustulose markings. 



Two specimens have been found partially preserving the bifurcate extension in 

 front, one being the upper and the other the lower side of the head; while two 

 others (one of which is represented, fig. 1 , Plate lxxvi ) have this process broken 

 off. In one specimen, a single eye is pretty well preserved, but not in such a degree 

 of perfection as to enable one to count the entire nnniber of lenses. 



PL.\TE LXXV. 



Fig. 2. The inner side of the crust of a pygidium, showing the thickened border and a part 

 of the posterior spine. 



PLATE LXXVI. 



Fig. 1. The head of a specimen, natural size. The frontal process is broken off; and the 

 continuation, as represented, is drawn from fig. 2. 



Fig. 2. An imperfect head preserving the glabella (which is distorted by pressure), the bases 

 of the eyes, and the frontal process. The extremities of the bifurcations are broken 

 off, and their true extent is not known. 



Fig. 3. The under side of the test of the head, preserving the anterior border and the frontal 



process. 

 Fig. 4. The eye and part of the cheek, from another specimen. 

 Fig. 5. Profile view of the same, with the posterior portion extended. 



Fig. 6. A portion of the eye-;8urface enlarged, showing the lenses and the rounded grains 

 between. 



Fig. 7. The pygidium, showing the elongate caudal spine. 



Fig. 8. Profile view of the same. 



Fig. 9. Enlargement of the surface. 



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

 group : Schoharie. 



TiieliaH l>io-8byi ( n. s.). 



Plate LXXVII. Fig. 1-8. 



Head abruptly arched, the anterior contour parabolic ; frontal limb nar- 

 row, with a strongly defined groove. The median lobe of the glabella 

 ventricose anteriorly and in the middle, narrowed and somewhat 

 depressed behind, becoming nearly flat towards the occipital furrow ; 

 width, in front, four times as great as at the base ; rising very promi- 

 nently above the other parts of the head, the greatest elevation about 

 half way from the occipital furrow to the frontal margin. The anterior 



