46 NEW YORK STATE MUSEUM 



which, as he suggests, might represent the young of T . s e t i - 

 ■cornis, and which, judging from his drawings (specially 

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

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

 species, congeneric with Tretaspis reticulata, 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 1 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. 

 earinatus is supposed to come from regio Da, both carinate 

 forms are approximately homotaxial. 



Trinucleus seticornis occurs in Scotland and Ireland 

 in beds referred to the Caradoc age, in Sweden in regio Da, and in 

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

 £ven the Normans kill shale beds, in which the conglomerate 

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

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

 1 e n t u s , from regio Bd, Norvegiae, the species which differs 

 most from the rest of the group. 



Tretaspis diademata sp. nov. 

 PI. 3, fig. 12, 13, 14 



A specimen of Tretaspis which was found in a black lime- 

 stone pebble associated with Tretaspis! reticulata 

 and Ampyx hastatus 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 



i Lindstrom's 2d ed. 1878. pi. 34, fig. 3. 



