TRENTON CONGLOMERATE OF RYSEDORPH HILL 69 



angular outline with about 14 annulations on the axis, and about 

 10 ribs with pleural grooves. The species was originally 

 described from the Trenton limestone of Ottawa. Dr Clarke 

 figures a specimen from the Trenton limestone and reports it 

 from the middle Trenton of Minnesota, and in a variety with 

 extremely broad frontal lobe of the glabella from the Hudson 

 river group at Cincinnati. As no mention of this form is made 

 in other reports of Trenton faunas, it is either often overlooked 

 by failing to be distinguished from Pterygometopus 

 callicephalus or is of rare occurrence, as asserted by 

 Billings. (Group 7) 



pterygometopus Schmidt 

 Pterygometopus eboraceus Clarke. Geol. Minn. Pal. v. 3, pt 2, 



p. 728 

 PI. 4, fig. 15 



Two cranidia, obtained from a gray crystalline limestone boul- 

 der, were found to agree with the description and figures of the 

 corresponding parts given by Dr Clarke of a new species, col- 

 lected at Rawlins Mills in Saratoga county. The important 

 features which demonstrate the identity of the forms from Ryse- 

 dorph hill with that species, are the convexity of the median 

 portion between the first and second lobes, the short incised 

 character of the separating furrows at their inner extremities, 

 and the confluence of the lobes along the dorsal furrows, as well 

 as the presence of a conspicuous tubercle at the center of the 

 occipital ring. 



The occurrence of this form in the pebbles of the Rysedorph 

 hill conglomerate seems to be of special interest, as the species 

 has thus far been found only in the Trenton limestone at Rawlins 

 Mills, hence in beds which outcrop only a relatively short 

 distance to the north, and which may be contiguous with those 

 from which these boulders were derived. 



A new species more closely related to P t. e b o raceus than 

 to any other species has lately been described from the Trenton 

 of Silliman's Fossil Mount on Frobisher bay in Baffin Land. 

 (Group 7) 



