TRENTON CONGLOMERATE OF RYSEDORPH HILL 59 



furrows, and that this difference may easily be overestimated. It 

 is of special interest that R. tuberculatus occurs in stages 

 2 and 3 of the Tramore limestone, which is said to underlie 

 Glenkiln shales, homotaxial with the Normans kill graptolite 

 shales. 



There is still another European form which well bears a com- 

 parison with our fossil ; this is Brachypleura sexline- 

 a t a Angelin (pi. 9, fig. 13) which in relative length and width 

 oif glabella, character of eye lobes, specially at the posterior end, 

 tuberculation of glabella and extent of glabellar furrows closely 

 agrees with R. linguatus, while it differs in having a 

 much narrower frontal glabellar lobe, and, judging from the draw- 

 ing, in the absence of tuberculation on the neck ring. This 

 species is from the limestone of the Kinnekulle in Vestrogothia. 



asaphus Brongniart 

 1 Subgenus isotelus De Kay 

 Isotelus maximus Locke 

 2d an. rep't geol. sur. Ohio. 1838. p. 246 



Oranidia, eyes, pygidia, hypostomata and large genal spines 

 of this trilobite are extremely frequent in the gray crystalline 

 limestone pebbles, in some parts so common as to exclude other 

 fossils. They are less frequent in the black compact limestone 

 pebbles and in the cement, and none has been found in 

 the reddish gray limestone with ostracods. The numerous 

 spines would indicate that the prevailing species is Isotelus 

 maximus in distinction from Isotelus g i g a s , but, as 

 Dr Clarke 1 has pointed out, the cheek spine in these asaphids is 

 to be regarded rather as a character of immaturity, diminishing 

 in size as the adult condition is approached, than as one of critical 

 value for specific separation. 



The presence of muscle scars in the pygidia of this species 

 observed in material from Rysedorph hill, has already been 

 mentioned. Isotelus maximus ranges from the Tren- 

 ton into the Richmond beds; Isotelus gigas is reported 

 from the Chazy of Canada. (Cement and groups 5, 7) 



» Geol. Minn. Pal. 1897. v. 3, pt 2, p 701. 



