I20 NEW YORK STATE MUSEUM 



Dalmanites micrurus Green (sp.) 



Plate 9, figures 1-3 



Asaphus micrurus Green. Monogr. Trilobites N. Am. 1832. p. 56, fig. 3 

 Dalmania micrurus Hall. Palaeontology of New York. 1859. 3 : 359, pi- 74, 



fig. 13-20 

 Dalmania pleuroptyx Hall (not Green). Idem. pi. 74, fig. 1-6, 9-12 

 Dalmanites micrurus Hall & Clarke. Palaeontology of New York. 1888. 



7 : 29 



The original specimens of Green's species Asaphus micrurus and 

 A. pleuroptyx, both of which are in the State Museum, are pygidia. 

 The former name was applied to a large tail ' which the author thought was 

 from the Trenton limestone, though Hall corrected this error with the aid 

 of the accompanying fossils in the matrix of the specimen. It is plainly 

 from the Helderbergian Coeymans limestone, probably of the Schoharie 

 valley. The original of the latter species, D. pleuroptyx, is a small 

 pygidium from the New Scotland beds of the Helderberg. In later collec- 

 tions we have found that this style of pygidium is that prevailing in the 

 Helderbergian and appertains to the type of cephalic structure illustrated in 

 Palaeontology of New York, v. 7, pi. 11 A, fig. i, under the name D. pleu- 

 roptyx. When Hall was describing the Helderbergian trilobites (Pal. 

 N. Y., V. 3) chiefly from material gathered in the Schoharie valley, he allo- 

 cated to the D. pleuroptyx tail a very different style of cephalon, 

 namely that now ascribed by us to D. micrurus. He had then but a 

 single and extremely young entire individual of this type wherein it was 

 practically impossible to tell which species the pygidial characters indicated, 

 and it is a singular fact that notwithstanding the abundance of these Hel- 

 derbergian remains, the one (D. micrurus) in the Coeymans and the 

 other (D. pleuroptyx) in the New Scotland beds, but a single entire 

 specimen of each is known to us. As the original tail of D. pleuroptyx 

 is from the New Scotland beds and we know the rest of the test structure it 

 follows that all the cephala referred by Hall \op. cit^ to that species, as they 

 are of a distinct type of structure and as these two species are the only 

 Dalmanites known from the Helderbergian fauna, belong to the species 

 D. micrurus. 



Such cephala we have from the Grande Greve limestones. The type 

 of structure presented therein is notable for two features, (i) entire inde- 

 pendence of the lateral glabellar lobes, (2) absence of ornament on the 

 frontal border. The outline is regularly semielliptical with rather short 

 genal spines. The surface is moderately elevated with abrupt slopes 

 beneath the eyes. The dorsal furrows are deep where they border the 



'Green, regarding the pygidium as "tail and abdomen," gave the name "micrurus" 

 on account of the small caudal spine, 



