TRENTON CONGLOMERATE OF RYSEiDORPH HILL 47 



therefore om the crest of the ridges. At the genal angle the 

 ridges become rather abruptly dissolved into a crowded irregular 

 mass of perforations (tubercles in the cast). Other differences 

 between this and the preceding species are the considerably 

 less width and almost vertical position of the limb in the frontal 

 region and the greater prominence of the cheeks. The cheeks 

 and glabella are finely reticulate. 



Dimensions. Width of cranidium 15 mm; length 5.8 mm 1 ; great- 

 est width of glabella 3.1 mm. 



Horizon and locality. Pebble of black limestone in Kysedorpb 

 hill conglomerate. (Group 5) 



Observations. The writer was at first inclined to consider this 

 form as only a variety of T . reticulata. As, however, 

 forms differing from T. s e t i c o r n i s in the same development of 

 the limb have been described from corresponding beds in Norway 

 and Great Britain, it seems opportune to separate also this form 7 

 in order to emphasize the fact of the occurrence of this 1 type 

 together with that of T . r e t i c u 1 a t a in approximately homio- 

 taxial beds on this and the other side of the Atlantic. It is, 

 however, to be noted that, both in T . seticornis and T . 

 reticulata, the perforations show more prominent arrange- 

 ment in concentric rows, and less distinct radial arrangement; 

 hence these forms probably represent only diverging branches from 

 the principal stock, the common and widespread T. set i c o r n i b 

 in Europe and T. reticulata in America. Angelin's form T, 

 foveolatus (pi. 41, fig. 2) is from Da Norvegiae, and described 

 as follows: T. capvte subtiliter favosa, limbo radiato, fronte utrinque 

 foveolis (?), apice subglobosa, punctis ordinariis majusculis. In this 

 form the radial arrangement of the perforations extends over 

 the whole surface of the limb. A corresponding form, occurs in 

 the Llandeilo and Caradoc beds of Great Britain, and was first 

 described by Murchison as Tri nucleus fimbriatus (?) ; 

 later its characters were elucidated moire fully, and a complete 

 specimen from the Llandeilo flags figured by Sedgwiick and 



