50 NEW YORK STATE MUSEUM 



Dimensions. Width of cranidium 14.2 mm, length to base of 

 rostrum 7.5 mm, width of glabella 5.2 mm, width of largest 

 pygidium 5.5 mm, length 2.5 mm, width of axis 1.8 mm. 



Horizon and locality. In the black compact limestone pebbles 

 of Trenton age, in the conglomerate of Ryserdorph hill. (Group 

 5,6) 



Observations. This form differs from the only other Trenton 

 species, Ampyx americanus Saff ord and Vogdes, 1 in the 

 large anterior extension of the glabella beyond the fixed cheeks, 

 this being a longifront,the other a brevifront, using subdivisional 

 terms proposed by the discoverer of A m pyx americanus^ 

 and in having a strongly convex glabella without the oblique 

 furrows of the western Trenton form. Our species is much more 

 similar to Ampyx h a 1 1 i Billings, from the Chazy limestone 

 of Canada and Vermont, with which it has in common the elong- 

 ate convex rather strongly carinate glabella. and the shape of 

 the neck segment, but from which it differs in having a relatively 

 shorter glabella extending hardly beyond the fixed cheeks, and 

 by the semioval pygidium with distinct pleurae. Ampyx 

 n o r m a 1 i s from the Canadian Quebec beds, has the fluted 

 rostrum and the rounded glabellar pits, but differs from A. 

 ha status in its short glabella. The Rysedorph hill species 

 is much more closely similar to Ampyx r o s t r a t u >» 

 Sars (Ampyx sarsii Portlock) in general outline, keeled 

 glabella, long rostrum, long corniform cheeks, and according to 

 the detailed description by Pompecki, 2 the elliptic impression on 

 either side of the base of the glabella, while it differs in having 

 the cheeks relatively broader and less contracted in the anterior 

 part, and the pygidium more rounded. This closely related 

 form is described by Portlock (loc. cit. p. 258) from the 

 fossiliferous schists of Tyrone (Ireland) which are regarded as 

 older than the schists with Diplograptus p r i s t i s and 

 Graptolithus Sagittarius, corresponding to our Nor- 

 mans kill shales in which the conglomerate is interbedded. 

 Angelin describes the same species from the " regio Da Norvegiae 

 prope Christiania et in monte Kinnekulle Vestrogothiae" ; and 



i Acad. nat. sci. Phil. Proc. 1889. 4:166. 



2 Trilobiten fauna der Ost- und Westpreussischen Diluvialgeschiebe. 1890. p. 16. 



