442 Forty-fifth Report on the State Museum. 



evidently necessary to restrict the term Prionopeltis closely to 

 typical forms agreeing with Barrande's Ph. Archiaci and Ph. 

 striatus, for Novak has also shown good reasons for separating 

 from this association forms like Phaeton planicauda, Barrande, 

 and has given to this restricted group the name, Phaetonellus. 



The American species have a cephalon with a thickened, 

 usually elevated margin, continued into short genal spines. The 

 surface of the ante-lateral limb is concave, the eyes well forward 

 and close together as in Cyphaspis. The glabella has the form 

 of that in Arethusina, is short, ovoid, has two conspicuous basal 

 lobes, and bears the trace of a pair of short lateral furrows, which 

 are situated at about the mid-length of the glabella, and under 

 favorable circumstances in an internal cast, are seen to bifurcate 

 slightly at their proximal extremities. The number of the 

 thoracic segments has not been ascertained, but specimens found 

 of Ph. gemmceus, of the Hamilton group indicate that the num- 

 ber was not more than ten, and that the forms were proetoid in 

 this respect. The pygidium is always relatively large, subsemi- 

 circular in outline, the rhachis and pleura abundantly annulated, 

 from 7 to 12, on the former and from 6 to 8 on 

 the latter. The pleural annulations are subequally duplicate. 

 The rhachis does not extend to the margin. The surface is 

 tubercled, the tubercles being irregularly scattered over the 

 cephalon, and arranged in regular rows on the segments and 

 annulations. These tubercles sometimes take the form of 

 spinules (Ph. arenicolus, Ph. gemmceus) and extend beyond the 

 margin of the pygidium, but they seem never to have their 

 insertion on the margin itself. 



This group of trilobites which we propose to term Cordania 

 (Phaethonides cydurus, Hall ; type), may be said to show alliance 

 to Proetus in the structure of the pygidium and thorax, to 

 Cyphaspis in the cephalon generally, and to Arethusina in its 

 glabella in particular. It differs from the Tropidoooryphe of 

 Novak (Proetus filieostatus) in the latter having a proetoid, sub- 

 triangular glabella, comparatively large and distant eyes, and a 

 pygidium with less conspicuously duplicate annulations and 

 shorter rhachis. 



In American faunas this genus is well represented in species, 

 its earliest members being Cordania oydl/ura^ Hall (sp.), from the 



