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Ni:W YORK Sl'ATI-: MUSEUM 



juries have combined to make a complete analysis not only one of 

 great difficulty but one of danger to the specimen as well. The cir- 

 clet of five contiguous and similar plates next the proximal stem 

 joint is, however, clearly seen and the outlines of other plates of the 

 injured area may be easily followed. A partial analysis of this 

 syntype, showing five vertical rows of plates, is presented in text 

 figure 25. 



The other syntype is here designated as B and is illustrated by 

 text figure 22. This specimen shows some thirty and more ]:)lates in 



Fig. 22 Palaeocy stites dawsoni Bill. Syntype B. X3 

 Fig 23 Palaeocy stites dawsoni Bill. Apotype X3 



the vicinity of the mouth and anus. Early efforts to clean the speci- 

 men seem to have removed some portions of the plate surfaces, but 

 sutures and sutural canals are very clearly seen. Syntype B thus 

 supplies a large and important area for analysis and the plate 

 arrangement of this region is presented in figure 24. These two 

 syntypes were both collected by E. Billings from the Chazy of the 

 island of Montreal. 



With some specimens also collected from the Chazy of the island 

 of Montreal by E. Billings, but labeled Palaeocy stites 

 t e n u i r a d i a t u s Hall, is a third specimen of P. dawsoni 

 which is here made an apotype and is illustrated by figure 23. The 

 specimen is only a fragment but it presents us with a complete cross 

 section of the theca just below the anus. The ten vertical rows 

 are here represented by a zigzag circle of plates, a higher and a 

 lower regularly alternating with each other. Several plates .show- 

 above this ring but the plates nearest the mouth seem to be lost. The 

 epithecal canal coverings of this specimen have been removed by 

 purely natural processes and in so delicate a manner that their ex- 

 treme thinness is still manifest by their remaining edges. The 

 character of l)ntli cpilheral and sutural canals is revealed with excep- 



