TKlLOlilTr.S <3F THE ChAZV LlMESTONE. 363 



very prominent, not extending to the posterior end. The first annu- 

 lation of the axis extends clear across, and behind it are fifteen to 

 eighteen which show only on the sides. Along the top of the axis are 

 four or five pairs of nodes which are located at equal intervals along 

 its length. There is a single median protuberance at the posterior end 

 of the axis. On the pleura are four pairs of double ribs which turn back 

 nearly parallel to the axis. Each double rib consists of a smaller 

 anterior and larger posterior portion. The ribs end in short rounded 

 spines which extend only a very short distance behind the border and, 

 when these spines are broken, as is often the case, the margin appears 

 as if entire. Up near the axis each rib bears a small node. 

 Measurements. — Three pygidia : 



1. Length 4.5 mm.; width 3.75 mm.; length of axis 3.5 mm. 



2. Length 3.75 mm.; width 3 mm.; axis 3 mm. long. 



3. Length 6 mm.; width 5 mm.; axis 4.75 mm. long. 



From Cyhele {Encri/ii/nis) mints Billings, this species differs in 

 being more slender and in having only one annulation, instead of four- 

 teen, extending across the axis. 



To Cvbele winclielli Clarke, our species is very closely related, but 

 it has evidences of a great many more annulations on the axis than 

 are shown by that species. 



The only other American species, so far described, is Cybele sp. 

 Ruederman from the Rysedorph conglomerate. Only a fragment of 

 the anterior part of this specimen is known, but it differs from our spe- 

 cies in having the posterior annulations extending all across the axis. 



The rarity of Cybele in American faunas can be most plainly brought 

 out by noting that, so far, one nearly complete specimen has been 

 collected from the Trenton in Minnesota ; a fragment of a pygidium 

 from Rysedorph Hill, New York ; a few fragments of pygidia from 

 the Quebec group, in Newfoundland, and a dozen pygidia from one 

 locality in the Chazy limestone in New York. 



Formation and Locality. — All the specimens are from the quarries 

 near the road at Valcour, New York. 



Family CHEIRURID.^ Salter. 



Genus AMPHION Pander. 



Amphion canadensis Billings. (Plate 14, figures 10-13.) 



Cf. Calymcne mtdtiiOita Hall, 1S47, Paleontology of New York, volume I, page 228, 

 plate 60, figure 3. 



