INVERTEBRATES. 349 



If it were true, as Meek and Worthen asserted, that in "Codon- 

 ites" the five or six upper joints became anchylosed in more adult 

 specimens, and were transformed into solid plates, it is very singu- 

 lar that no transition forms have ever been found in this or any 

 other allied species. I think a metamorphosis like this would have 

 undoubtedly left traces of the columnar joints in the growing 

 animal, especially since the modification, as we may safely suggest, 

 must have taken place gradually, and joint by joint; but although 

 I have examined more than fifty specimens of this species, I could 

 not find the remotest traces of former stem joints, or of a suture; 

 all that I have been able to discover is a slight angular depression 

 around the lower end of the cup. This depression, which has some- 

 what the appearance of a suture, is caused simply by the more rapid 

 spreading of the upper portions of the basals. Such at least is the 

 case in some species of Codonites, Cadaster and Troostocrinus, in 

 which the base appears as if it might be bicyclic, but actually is 

 monocyclic, and in which the lower part is almost cylindrical, and 

 resembles an elongate columnar joint, while the upper part is 

 conical. 



It seems to me that this upward spreading of the basals can be 

 naturally explained by the growth of the animal. The form gener- 

 ally throughout the Blastoids is in a young specimen more elongate 

 than in the adult, and after attaining a certain growth, the calyx 

 increases in height comparatively little, while the ambulacra still 

 grow considerably longer. This disproportion in the growth of the 

 different parts is equalized by the increase of the body in width, by 

 which the ambulacra attain a greater ' curvature, pushing the basals 

 and partly the radials, from a fairly sloping position to a more 

 horizontal one, as shown in the following species, of which I have 

 examined a large number of specimens in all stages of growth. 



In the young Orophocrinus stelliformis, the ambulacra occupy only 

 the upper truncate side of the body, the lower portions are turbinate 

 with nearly straight sides ; in very old specimens, however, the am- 

 bulacra curves so strongly, and reach down so deeply, that the radial 

 lips were brought into a horizontal position, almost to the level of 

 the basals, and the sides of the body became concave, thereby push- 

 ing the upper portions of the radials in a more outward direction. 



Schizoblastus (Granatocrinus) melo 0. & Shum. is, in its younger 

 stages, elongate-ovate, in medium sized specimens subglobose to glo- 

 bose, and in large specimens depressed globose. The same modifi- 



