I 
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 
f 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 and locality. In the pentamerus and shaly limestones of the 
Lower Helderberg group : Albany and Schoharie counties. 
Dalmaiiia tridens ( n. s ). 
Plate LXXY. Fig. 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 ShumArd ( Missouri Geo¬ 
logical Report, 1855, Part n, pa. 199, pi. b, f. 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. 
[ Palaeontology III.] 
46 
