2 PKOCEEDINGS OF THE NATIONAL MUSEUM vol. 75 



the fourth primibrach, though one arm of each of two specimens has 

 the bifurcation on the third primibrach. The two rami thus formed 

 are of equal size and remain simple. Long, stout ramuli are borne 

 by the rami on alternate sides on each second brachial. The food- 

 grooves of the arms are covered by two rows of small interlocking 

 ambulacrals. In the posterior interradius there is one anal plate in 

 the cup. This is plate X, which is of approximately the same size 

 and proportions as the adjacent radials. The ventral sac is relatively 

 heavy and round in cross section. In its basal portion on the poste- 

 rior side there is a median line of heavy plates, four or five in number, 

 scarcely to be distinguished from brachials except for the fact that 

 they are somewhat narrower. It is only by careful cleaning and 

 examination that X with its sequence of heavy median tube plates 

 can be distinguished from a radial and its series of primibrachs. The 

 surest test in these small specimens is the relation of plate X to the 

 basals. The radials, of course, alternate with the basals, while X rests 

 squarely on the upper truncated face of the posterior basal. The 

 column is round and tapers slightly for a short distance distad. It 

 then maintains a uniform diameter so far as seen. The column is 

 composed of alternating thick and thin columnals, with a tendency 

 toward a grouping into nodals and internodals. 



Genotype. — The genotype is Pagecrinus gracilis, new species, the 

 only known species referable to the genus. 



Horizon. — The type species is from the Middle Devonian of 

 Indiana. 



PAGECRINUS GRACILIS, new species 



Of this form four reasonably complete crowns in an excellent state 

 of preservation, two less perfect crowns, and several fragmentary 

 specimens showing details of arm-structure are available for study. 



The species is a small one, one of the largest crowns giving a 

 height over all of but 20 millimeters. In this specimen the dorsal 

 cup is 5.5 millimeters in height. Further measurements of this 

 specimen are as follows: 



mm. 



Diameter of dorsal cup at base of arms 2. 3 



Diameter at base of dorsal cup 1.6 



Height of IBB 1.9 



Width of IBB 1.1 



Height of BB 2.7 



Width of BB 1.3 



Height of RR 1.2 



Width of RR 1.1 



Height of anal X 1-1 



Width of anal X .9 



As shown by measurements, the dorsal cup is slender and tapers 

 slightly from the upper margin to the base. 



