the Morphology of the Blastoidea. 231 



Codasfcr vel Codonastei; M'Cov, Brit. Pal. Foss. 18-51, fasc. i. p. 122, 



t. 3 D (expl). 

 Codonasfe)-, F. Romer, Wieginanu's Aicliiv fiir Naturgescliichte, 18ol, 



xvii. Bd. i. p. 381. 



Ohs. Without absolutely redefinino- Codaster^ we may say 

 that, on the whole, we accept M'Coy's definition as accurately 

 descvibino- the characters of the genus. Some few emenda- 

 tions and additions are necessary. For instance, the radial 

 plates (McCoy's suprabasals) not only " reach to the trun- 

 cated summit," but they are more or less inturned at the edge 

 of the summit towards the apex, so as to form limbs in the 

 usual way, which enclose narrow radial sinuses like those of 

 other Blastoids. Oral plates also are present, appearing as 

 diamond-shaped plates on the truncated summit in well-pre- 

 served specimens. Four of these bear along their median 

 line tlie " thick, rapidly tapering ridges " of M'Coy, which 

 are in no way an abnormal structure, but only represent the 

 crests of the orals (and sometimes the combined orals and 

 radials) of other genera. 



So far as our own researches have gone, we have been quite 

 unable to detect the supplemental basals described by Mr. S. 

 S. Lyon * in any species examined by us. The " rough 

 parallel striai " and the '^ impressed lines " between them of 

 M'Coy appear to have been a great stumbling-block to the 

 earlier investigators of this genus. Lyon remarks, " the de- 

 pressed triangular intervening spaces are filled with seven or 

 more thin pieces lying parallel to the pseudambulacral fields, 

 articulating with the summit of the second radials, and the 

 prominent ridge lying between the pseudambulacra3. These 

 pieces were evidently capable of being compressed or de- 

 pressed "t- It is almost needless to observe that the view 

 ascribing to the hydrospiral grooves the nature of distinct 

 pieces is uq longer tenable. 



In 1861 Prof. James Hall observed that the striated inter- 

 radial spaces of his Codaster Whitei " appear to be composed 

 of separate linear plates like the pectinated rhombs of the 

 Cystideans ; and in one place, where broken through, they 

 are seen to be discontinued almost to the inner face of the 

 substance, giving the appearance of numerous thin parallel 

 lamellae" J. These remarks may be said to have foreshadowed 

 the important discoveries which were afterwards made by the 

 late Mr. llofc, and published in 18G5. He found, by cutting 



* D. 1). Owen's 3rd Kentucky Report, p. 493. 

 t Loc. cit. p. 494. 



X Boston Journ. Nat. History, 18G1, vii. no. 2, p. 327.. 



17* 



