TRENTON CONGLOMERATE OF RYSEDORPH HILL 47 



therefore on 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; great- 

 est width of glabella 3.1 mm. 



Horizon and locality. Pebble of black limestone in Rysedorph 

 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. seticornis in the same development of 

 the limb have been described from corresponding beds in Xorway 

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

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

 together with that of T . reticulata in approximately honio- 

 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. seticornis 

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

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

 as follows: T. capite siihtiJifer favoso. Umbo radiato, f route utrinque 

 foveoUs (f), apke suhglobosa, putwtis ordinariis majuscuUs. In this 

 form the radial arrangement of the perforations extends over 

 the whole surface of the limb. A coiTesponding form occurs in 

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

 described by Murchison as T r i n u c 1 e u s f i m b r i a t u s i'?! : 

 later its characters were elucidated more fully, and a complete 

 specimen from the Llandeilo flags figured by Sedgwick and 



