338 PALJCOiNTOLOGY OF NEW-YORK. 



This species has usually been referred to Dalmania ( Amphus ) hausmanni by 

 American and European authors; but a comparison with tlie excellent figures of 

 Barr.\nde, and with his minute description, shows a diti'trence in form of the py- 

 gidium, which, in our species, is more triangular; in the prolongation'of the posterior 

 angles of the head; in the number of lenses in the eye (the European form having 

 from 420 to 680); and in the articulations of the axis of the pygidium, which, in 

 the P. hausinanni, has eighteen or nineteen, and thirteen or fourteen ribs in each of 

 the lateral lobes. 



PLATE LXXIV. 



Fig. 1. A young specimen which is extremely flattened." 



Fig. 2. The same enlarged, showing more distinctly the characteristic features of the species. 



Fig. 3 & 4. The head of a young and of a half-grown individual, which are probably of this 

 species. In the fragmentary condition of specimens, I have at present no means 

 of knowing which of the heads may belong to this or to the succeeding species. 



Fig. 5. The original preserves the central portion of the head, with one eye nearly entire. 

 The posterior angles arc completed from another specimen. 



Fig. 6. The pygidium of a young specimen. 



Fig. 7. The pygidium of a larger individual. 



Fig. 8. A larger individual in which seventeen annulations are distinctly visible in the axis 

 (and an eighteenth is very faintly indicated), and thirteen ribs in each lateral 

 lobe). 



Fig. 9. Profile of the head, showing the form and elevation of the eye. 



Fig. 10. The eye enlarged. 



Fig. 11. A portion of the surface still farther enlarged. 



Fig. 12. A magnified portion of the eye, where the lenses have been removed by weathering. 



PLATE LXXV. 



Fig. 1. The specimen is a cast preserving a part of the head, the axis and one lateral lobe 

 of the thorax, and a part of the pygidium. From the condition of the specimen, 

 it cannot be positively referred to this species, though there can be little doubt 

 of its identity. 



Giological posifiofi and locality. In the shaly limestone, and sometimes in the 

 pcntamerus limestone, of the Lower Ilelderberg group : Helderberg mountains, 

 Schoharie, Carlisle, Catskill and Becraft's mountain, and in the same geological 

 position in Pennsylvania and Virginia. 



The accompanying figure is from the mould of a pygidium, in the axis of which 

 about fifteen articulations may be counted, the posterior ones being obliterated. It 

 is evidently the pygidium of one or the other of these species, and, from its great 

 breadth, I am inclined to refer it to D. pleuroptyx. It is interesting as showing the 

 large size to which the animal has Sometimes attained. 



