58 ROYAL SOCIETY OF CANADA 



Detached pleura» are found which show that lon^ spines were 

 attached to the ring in the Joints of the racliis, in some cases these spines 

 were as long as the straight part of the thoracic segment to which they 

 were attached. 



Development of the Youmj. — Young heads 5^ mm. long do not ditfer 

 much from the adult, except in the proportion of i)arts ; the rachis of the 

 head shield at this stage is more than twice as long as wide ; when grown 

 to the size of 7^ mm. this part is two-thirds wider than long, but in the 

 full size (20 mm.) it is only a half longer than wide. 



The middle i)iece of the head in this species considerably resembles, 

 some of the species of Dicellocephalus, Hall k Whitfield, from Wisconsin.' 



The type of this species was found by Mr. Walcott in the Eureka 

 district of Central Nevada, and Roeminger's form appears to be a variety. 

 The following differences may be noted. The head of the Mount Stephen 

 fos.sil is twice as long as the width of its glabella ; the Eureka form is 

 two and a half times as long ; in the former the dorsal suture approaches 

 the glabella to one quarter of its width, in the latter it almost touches 

 the glabella ; also in the former the glabella is proportionately shorter; 

 and the e3'e-lobe more strongly arched.- 



The species in the Cambrian of the west of Europe which most nearly 

 approaches this species in the form of the thorax aud pygidium is 

 Parabolina spinulosa ; in that, however, the position and shape of the eye 

 is quite different. 



OGYGIA Brongniart. 

 Oqygia (Ogygopsis) Klotzi, Eoem. 



Ogygia Kotzi, Roem., Acad. Nat. Sci., Phil. Proc, 1887, p. 12, pi. i., fig. 1. 

 Ogygopsis Klotzi, Wale, U. S. Nat. Mus. Proc, 1888, p. 446. 



Many examples show the outlines of this species ; the size and 

 details of the parts appear to be as Roeminger has described them, 

 though there are some differences. The severe fîattening of the tests in 

 the shale has modified the surface features considerably, making promi- 

 nent, portions of the test which were not so when the animal was 

 living. The eye-lobe is an example; this in less uncompressed heads 

 rises gradually to the margin, but in most a narrow rim is elevated 

 along the margin, because this part of the lobe was a thickened arch. 

 The ocular fillet appears to have been brought into unusual prominence 

 by the same cause. Upon these two features Mr. Walcott has foumled 

 his genus. There is, however, reason for a sub-generic distinction in the 

 shape of the eye-lobe, which is not nearly so strongly arched as in the 



' See Preliminary notice of Fauna of Potsdam Sandstone [in Wisconsin], Hall 

 & W., PI. X., liKs. 1 and i. 



" U. S. Geol. Surv., Memoirs, viii., pi. ix., fig. 22, 



