332 
PALAEONTOLOGY OF NEW-YORK. 
head, and another one preserving the head and part of the thorax and several 
articulations of the pygidium, and a separate pygidium; but the whole are so muti¬ 
lated as to afford very unsatisfactory evidence of the entire character of .the species. 
Fig. 5. The head of this species. 
Fig. 6. A fragment preserving the head and part of the thorax. 
Fig. 6 a. Lateral view of the same. 
Fig. 7. The pygidium of another individual. 
Fig. 8. An enlargement, showing the surface marking. 
Geological 'position and locality. In the pentamerus limestone of the Lower Hel- 
derberg group : Schoharie county. 
Momaloiiotus vamueisii (n. s.). 
Plate LXXIII. Fig. 9 - 14. 
Head unknown. 
Thorax long : sides subparallel, the middle lobe flattened on the exterior 
surface ; articulations arching forward; longitudinal furrows faintly 
defined, being a simple undulation in the articulations; lateral lobes 
narrow, the articulations bent abruptly downwards at'the sides. 
Pygidium subtriangular with the articulating side much longer and broadly 
curving, extremely convex : axis prominent in the young specimens, 
and becoming subdued in older ones; width, at its upper extremity, 
equal to that of each of the lateral lobes. Annulations fourteen or fif¬ 
teen in the cast, and twelve ribs visible on each of the lateral lobes. 
Surface of the test punctate and striato-punctate : cast punctate. 
This species is known from three specimens of the pygidium (two of which are 
imperfect at the posterior extremity), and a fragment of the thorax; no specimens 
of the head having come under my observation. The thorax differs from the Niagara 
species in the forward arching of the articulations of the axis, while those of the 
lateral lobes are thicker towards their extremities. 
The pygidium of this species differs from that of H. delphinocephalus in the lesser 
prominence of the base of the axis and its greater number of articulations, which 
are more distinct, and the lower margin of each one more abrupt; and while we 
have in the lateral lobes of the Niagara species six or seven, and rarely eight or 
nine ribs, there are in this species twelve, counting in both instances the upper one, 
which is usually covered by the last thoracic articulation. 
