ON A NEW GENUS AND SPECIES OF BI.ASTOIDS. 79 



In the course of their remarks they made the peculiar statement that 

 the lower series or supplementary basals "were in adult specime?is of 

 Codonites stellifonnis as solid as 7c>e find them in Pentre mites; young in- 

 dii'iduals, however^ show clearly that they are actually composed of five or 

 six of the upper joints of the column, enlarged and anchylosed together." 

 Meek and Worthen undertook to prove this by a moderately small 

 specimen, in which five or six joints of the column were preserved, and 

 in the same direction divided longitudinally into three sections. It 

 should be stated that the specimen, which was formerly in my collec- 

 tion — now in the Museum of Comparative Zoology at Cambridge — 

 is not much below medium size, and, therefore, cannot by any means 

 be called a very young specimen. The column, as far as preserved, 

 consists, as in most Blastoids, of remarkably short joints with sharp 

 edges, and the joints are separated by rather deep notches; the longi- 

 tudinal sutures are not shown distinctly, but probably do exist in the 

 specimen. 



If it were true, as Meek and Worthen asserted, that in '■'■ Codoftites" 

 the five or six upper joints became anchylosed in more adult speci- 

 mens, and were transformed into solid plates, it is very singular 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, took place grad- 

 ually, 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 somewhat the appearance of a suture, is caused 

 by the more rapid spreading of the upper portions of the basals. 

 Such, at least, is the case in some species of Codonites, Codaster, and 

 Troostocrinus, in which the base appears as if it might be dicyclic, but 

 actually is monocyclic, and in which the lower part is almost cylin- 

 drical, and resembles an elongate columnar joint, while the upper ])art 

 is conical. 



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

 urally explained by the growth of the animal. The form generally 

 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 



