382 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



apparently being more augmented by addition to its external face than to its 

 lateral faces, so that the ratio of its breadth at its inner and its outer margins instead 

 of being, as at the conclusion of pentacrinoid life, about as two to three, comes to be 

 only as one to three, the shape of its dorsal face being thus changed from a trapezoid 

 to a triangle with its apex truncated. Concurrently with these changes we find 

 that the various ridges and fossse on the external and ventral faces of the plate for 

 the attachment of the muscles and ligaments by which it is articulated to the first 

 primibrach are gradually developed into the form they present in the adult, and 

 that the characteristic ridges and furrows of its internal face, with the prolongations 

 that connect it with the ventral face of the rosette, make their appearance. All 

 these features are marked out when the size of the plate is still minute as compared 

 with that which it ultimately attains." 



