LOWER HELDERBERG ROCKS. 361 



the geological position of the specimen to be in the Lower Helderberg group; while 

 a similar specimen, though less perfect, in the same collection (that of the Albany 

 Institute), is marked as from the Helderberg mountains, Albany county. 



Fig. 13. The pygidium of a young specimen, contrasting with fig. 6 in the number of an- 

 nulations of the axis and ribs in the lateral lobes. 



Fig. 14. A small pygidium having fifteen ribs on each lateral lobe, and twenty annulations 

 of the axis. 



Fig. 15. A fragment of a similar pygidium, on which the test is very perfectly preserved. 



Fig. 16. A larger pygidium from which the test has been removed, leaving the cast punctate. 



Fig. 17. Profile view of the same. 



Fig. 18. An enlargement to show the surface markings, from fig. 15. 



Geological position aiid locality. In the pentamerus and shaly limestones of the 

 Lower Helderberg group : Albany and Schoharie counties. 



Daliuaiiia trideiis ( n. a.). 



Plate LXXV. Fiq. 3, 4, 5 & 6. 



This species is known only from some fragments of the head, which show the 

 lower side of the test : one specimen preserves the cavity of the eye and the lower 

 side of the glabella. The frontal process is strong, somewhat flattened and trifurcate 

 at the extremity; the divisions short and strong. The surface of the frontal process 

 is evenly granulose, the under side of the glabella showing marks of larger pustules. 

 The specimens present some variety in the extension of the frontal process, but 

 which does not appear to be of specific importance. 



This species differs essentially from D. tridentifera of Shumakd ( Missouri Geo- 

 logical Report, 1855, Part n, pa. 199, pi. b, {.8 a, b ), in the extension of the 

 frontal process. 



Fig. 3. The under side of a portion of the head, showing the cavity of one eye and the 

  extension of the frontal process. 



Fig. 4. A fragment of the lower surface, showing the marginal limb on one side and the 

 frontal process. The abruptness of the junction of the process with the marginal 

 limb, as represented in the figure, is due to an imperfection in the specimen at 

 that point. 



Fig. 5 & 6. Fragments of the marginal limb and the frontal process from the lower side, 

 with portions of the surface enlarged. 



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

 group : Schoharie. 



[ Pal.«ontolooy III.] 46 



