28 PALEONTOLOGY OF NEW YORK. 



DAL M A N ITES, Barrande. 1852. 



H A U S M A N N I A , n. s.-g. 



Dalmanites (Hausmannia) pleuroptvx. 



PLATE XI A, FIG. 1-3. 



Asaph \tyx, Greek. Monog. Trilob. North Amer., p. 55. 1832. 



IX, Hall. Pal. N". Y., vol. in, p. 356, pi. 74, figs. 5 1 9 ? (not figs. 1-4, 6-8, 10-12) ; pi. 75, 

 fig. 1 1 1859. 



Tins species, the most abundant of all the trilobites of the Lower Helder- 

 berg faunas, has been found in the Oriskany sandstone of Canada, associated 

 with Spirifera arreda, Streptorhynchus (Ortkis) hipparionyx, Phacops cristata and 

 Dalmanites anchiops, and also in two well-defined examples of the pygidium, in 

 the Corniferous limestone of the State of New York. The species thus becomes 

 the only member of the trilobitic fauna of the Lower Helderberg known 

 to have continued its existence into the Upper Helderberg formations. 

 Its occurrence in Devonian horizons affords the opportunity of suggesting 

 some corrections of the previous identifications of the species The two species, 

 I), pleuroptyx, Green, and J), micrurus, Green, both of which were established 

 upon pygidia, were recognized in the third volume of the Palaeontology of 

 New York, ami the differences between them were there pointed out. It is 

 nevertheless true, that while it is not difficult to select examples of such pygidia 

 as appear to he specifically distinct, the differences seem to disappear with 

 abundant material, so that upon the basis of the pygidia alone, the attempt to 

 separate the two species is exceedingly unsatisfaetory. The type specimen of 

 D. pleuroptyx was from the Lower Helderberg of the Helderberg mountains, 

 and extensive collections subsequently made from this prolific locality show 

 that the abundanl pygidia of this species are every where associated with cephala 

 heretofore undescribed, a specimen of which is here figured (pi. xi a, fig. 1). 



