NIAGARA LIMESTONE OF CHICAGO, ILLINOIS. 



87 



Actinocrlnus 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. cornigerm ; and was not improbably furnished, like 

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

 age. 



Megistocrintjs Owen and Shumard. 



Megistocrinus Marcouanus W. and M. 



Plate II. figure 5. 







8tf° 





a. Left anterolateral ray. b. Left posterolateral ray, 



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



1 Learning, after we had engaged in this investigation, that 

 Mr. W. H. Niles, of the Museum of Comparative Zoology 

 at Cambridge, was occupied in a reinvestigation of Crinou 

 dca with a view to publication, we should have preferred that 



our own specimens of that type should be worked up by him. 

 He has, however, insisted on our proceeding independently ; 

 and, having done so, we deem this statement demanded by the 

 courtesy which ought to prevail among co-laborers in science. 



