Hamhach — Revision of the Blastoideae. 27 



externally, as a single opening ( G. melo * and G. norwoodi), 

 though they divide into two distinct canals before passing 

 entirely through the plates. The typical forms of this genus 

 also have the interradial pieces proportionally much larger 

 than in the true Pentremites,'] though this is not a constant 

 character. 



" In the possession of numerous, extremely slender, thread- 

 like, simple arms, arranged along the pseudo-ambulacral 

 areas, this type also agrees (as might have been inferred from 

 analogy) with the true Pentremites, as we know from the 

 examination of a beautiful specimen belonging to Mr. Wachs- 

 muth. This specimen seems to be related to G. norwoodi^ 

 as near as can be determined, and shows at least thirty (there 

 are probably more) of these delicate, simple arms, arising 

 from each pseudo-ambulacral area, and extending up so that 

 the lower ones must be quite twice as long as the body. They 

 are all composed of equal joints, about as long as wide. So 

 far as we know, this is the only example of a specimen of this 

 type showing the arms, yet found. 



" As now understood, this genus includes species differing 

 materially in the comparative size of the interradial pieces, 

 the typical species having those pieces very large; J while in 

 another section of the genus, represented by such forms as 

 G. melo and G. no7nvoodi, they are as small as in Pentre- 

 mites. There are so many gradations in this character, how- 

 ever, that it does not seem to be possible to make it a means 

 of separating the species into two well defined sections." 



The first one to use the name Graiiatoamms was Dr. 

 Troost in a list of new species of Crinoideae from Tennessee, 

 which was read by Prof. L. Agassiz at the meeting of the 

 A. A. A. S. in 1850, and published in the Proceedings of 

 Amer. Assoc, Cambridge Meeting, p. (i2, but, as a descrip- 

 tion of the different species was never furnished, these names 



* hoc. cit. 274. Here no difference is made between the summit con- 

 struction of G. melo and G. norwoodi. 



t Meeli and Worthen. Geological Survey of Illinois, Vol. II., p. 275. 



X Referring evidently to the original species of Dr. Troost, G. cidari- 

 formis Meek and Worthen, Geological Survey of Illinois, Vol. II., p. 275. 



