NOTES ON UINTACRINUS SOCIALIS ORINNELL. 2 1 



the colony there is one arm which I have traced for seventeen inches, 

 and a comparison of its last distinguishable plates with the terminal 

 ones of the other arms makes it evident that the arms must have been 

 over two feet in length, as stated by Grinnell. They have well-de- 

 veloped pinnula^ beginning at the base of the arm, where they are very 

 large. They arise one from each plate, but alternating on the two 

 sides of the ambulacral groove. Grinnell described what he believed 

 to be interbrachial and interradial arms, but it seems certain that he 

 was in error in this respect, having mistaken the pinnula^ for these 

 arms. The interradials are usually seven in number. The first is 

 hexagonal and lies between the first and second radials of two series. 

 The other six are also hexagonal, and in life may have been arranged 

 in pairs, but are preserved in the specimens in irregular groups of 

 four. The interbrachials are two in number, heptagonal in shape, 

 and lie, respectively, between the first and second, and the second 

 and third secondary radials of the two arms. 



From the shape of the crinoid, its globose form and long, heavy 

 arms, one would hardly expect to find any of the ventral plates 

 exposed, and such is the case. Nor has it been possible to expose 

 them by dissecting away the plates. 



B. H. Hill. 



