REPORT OF THE DIRECTOR IQIO 



235 



use in recognizing the BB of this species and in orienting them. 

 Looking for the earHest position of this b.v. on the IB we find 

 it close to the point 

 marked a and about 

 0.6 milhmeter distant 

 from the suture. This 

 older portion of the IB 

 has added but 0.3 mil- 

 limeter to its side, 

 while it has added 2.3 

 millimeters to its orad 

 sutural faces. In other 

 words, the rate of 

 stereom addition to the 

 orad sutural faces was 

 nearly eight times as 

 great as was the rate 

 of addition to the lat- 

 eral sutures of the 

 plate. 



The growth has not 

 only been slight be- 

 tween the IBB, but it 

 has not extended to the 

 outer surface of the 



plate. The result is a Fig 14 Viewof aportionoftheholotypeof Palaeocrlnus 



stri'at US' Billings. From a photomicrograph, xio, and 

 well-marked groove showing r.post.B., r.post.IB. and r.ant.IB. The probable 



. forms of two of these plates at an early stage in their devel- 



widest next to the Orig- ':opment are, shown in outline. 



inal position of the proximal stem joint and becoming gradually 

 narrower and less deep orad. The groove is very smooth and shows 

 only faint vertical growth lines. This lack of growth at the suture 

 has left its impression on the B and has caused the groove to be 

 carried orad on the latter nearly to its center. The B has kept a 

 record of the cross section of the groove, as it appeared at the 

 suture, from its earliest stages to the time of death. This very char- 

 acteristic feature of a Palaeocrinus B, together with the slight 

 widening of the oldest aborad b.vs. (already mentioned) will be 

 referred to again under our remarks on P a 1 e o c y s t i t e s c h a p - 

 m a n i Bill. Using the different growth rate with reference to 

 direction, we have outlined a young IB in text figure 14. It ap- 

 proaches somewhat the character of a stem joint in that it is wider 

 than high and has no b.vs. on its lateral sutures. 



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