46 NEW YORK STATE MUSEUM 



which, as he 6ugj;estt^, uii«;hL represent the young of T. seti- 

 cornis, and which, judging from his drawings (specially 

 tab. 40, fig. 21) tshows a similar coarsely pitted *and reticulate 

 surface and similar outline of the cheeks. From all of these 

 species, congeneric with Tretaspis re t i c u 1 a t a , our 

 form differs not only in the strong reticulation, but also in the 

 development of a carina on the glabella of which no mention is 

 found in the descriptions, and no indication in the illustrations 

 of these species. 



Angelin^ however figures a form, T . c a r i n a t u s , which 

 has a median carina, passing along the whole length of the 

 glabella, and which also belongs to the subgenus Tretaspis 

 a fact' which serves to prove that this feature also was repre- 

 sented on the other side of the Atlantic basin, and, as T. 

 c a r i n a t u s is supposed to come from regio Da, both carinate 

 forms are approximately homotaxial. 



T r i n u c 1 e u s s e t i c o r n i s occui^ in Scotland and Ireland 

 in beds i-eferred to the Caradoc age, in Sweden in rcgio Da, and in 

 Bohemia, at a horizon which lies higher than that to which belong 

 even the Xormans kill shale beds, in w^hich the conglomerate 

 bed containing this fossil is intercalated. Our form is, hence, 

 older than all its congenei-s with the exception of T . b u c c u - 

 lent us, from regio Ba, Norvegiae, the species which differs 

 most from the rest of the group. 



Tretaspis diademata sp. nor. 

 VL 3, tig. 12, 13, 14 

 A specimen of Treta^-pis which was found in a black lime- 

 stone pebble associated with Tretaspis reticulata 

 and A m p y X h a s t a t u s presents the general appearance of 

 the former except that in the limb the perforations are not 

 arranged concentrically, but radially and so closely set as to pro- 

 duce high radial ridges and furrows. In the specimen the limb 

 is present only as an internal cast, and the perforations appear 



1 Lindstrtim's 2d ed. J8TS. pi. 34. flg. S. 



