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NEW YORK STATE MUSEUM 



Palaeocystites chapmani 

 (text fig. 20) l 



7. 8. 



7. 7- 



3- 4- 



0.7 mm 



mm 



Table 11 

 Palaeocrinus si riot us 

 r.ant.B (text fig. 8) 

 No. of b.vs. crossing common basal sutures 

 left or ad suture. . . . 

 " aborad suture. . 

 Distance apart (at suture) of oldest b.vs. 



crossing to IBB 



Dist. from orad to aborad angle 5.6 



across at orad ends of common sutures 4.8 

 aborad ends of common sutures 3. 1 



Length of left common suture 3 -7 



In addition to the tabulated resemblances it may also be seen : 



1 That the two longest and largest epithecal canals passing 

 aborad have no younger canals between them. 



2 That in P. chapmani we have the divergence of these canals 

 and the peculiar groove between them which we found in figure 14. 



3 That of the primitive canals the most prominent on P. chap- 

 mani are those passing orad or over to the probable RR of this 

 species, the next in prominence are those passing aborad or over to 

 the probable IBB, while the least prominent are those passing over 

 to the neighboring plates of the same circlet or to the BB. This 

 relation is the same as that expressed by the B of P. s t r i a t u s 

 shown in text figure 12. 2 



When we note how much the BB of Palaeocrinus 

 s'triatUs differ from each other, we must say that the corre- 

 spondences noted above very strongly suggest the idea that in this 

 type ofPalaeocystites chapmani we are dealing with a 

 single basal of Palaeocrinus s t r i a t u s. 



As P. chapmani appears to have its nearly horizontal canals 

 a little closer together than P. striatus, and as the upper 

 " radiating ridges " of Billings's description seem more raised and 

 rounded and the depression between them somewhat deeper than 

 in the type of P. striatus, we may for the present retain Bill- 

 ings's name and know his type as Palaeocrinus cnapmani 

 until additional specimens are found. 



1 The poor state of preservation of the plate of P. chapmani has no 

 doubt rendered some of these measurements inexact, but the error can hardly 

 1)C greater than 4 per cent. 



- This relative prominence apparently expresses relative age. though the 

 lessened rate of stercom formation along the common sutures of the BB 

 might make the primitive b.vs. crossing these sutures appear younger than 

 the first b.v. to cross to an IB. 



