NIAGARA LIMESTONE OF CHICAGO, ILLINOIS. 87 



ACTINOCRINUS Miller. 1 



Actinocrinus obpyramidalis W. and M. 



Plate II. figure 4. 



Body pentangularly obpyramidal ; radial series standing out in salient angles with 

 depressions between, deepening upward, and giving great prominence to the arm bases, 

 which are quite small, and exist in pairs. Dome arched, with the appearance (in our speci- 

 mens) of a broken proboscis a little nearer the centre than the anal side. 



Basal plates not seen ; radials three, the two lower hexagonal, the first a little larger than 

 the other two, and having its upper side shortest ; the third radial heptagonal, supporting a 

 pair of hexagonal secondary radials upon its upper sloping faces. The other plates of the 

 cup cannot be satisfactorily defined in our specimen. They give evidence of having been 

 elevated and sculptured. We have seen a specimen 1.75 inches high to the top of the dome. 



This species has all the general appearance of an Actinocrinus, and resembles such Carbon- 

 iferous species as A. quinquelobus and A. cornigerus ; and was not improbably furnished, like 

 them, with spines upon the dome. We know of no allied species of the same geological 

 age. 



MEGISTOCRINUS Owen and Shumard. 



Megistoerinus Marcouanus W. and M. 



Plate II. figure 5. 





a. Left antero-lateral ray. b. Left postero-lateral ray. 



c. Azygos side, with one half of the azygos interradials. 



1 Learning, after we had engaged in this investigation, that our own specimens of that type should be worked up by him. 



Mr. W. H. Niles, of the Museum of Comparative Zoology He has, however, insisted on our proceeding independently ; 



at Cambridge, was occupied in a reinvestigation of Crinoi- and, having done so, we deem this statement demanded by the 



dea with a view to publication, we should have preferred that courtesy which ought to prevail among co-laborers in science. 



