1879.] NATURAL SCIENCES OF PHILADELPHIA. 357 



massive and simple arms, and the exceedingly slender column. 

 A comparison, however, of all the species that have been referred 

 to the two genera discloses the peculiar fact, that some of them 

 disagree in certain other characters which we have heretofore, in 

 connection with other groups, and apparently with good reason, 

 considered to be of generic value. Among these we may mention 

 the variation in the size of the proximal or underbasal plates, in 

 the number and arrangement of the anal pieces, and in the form 

 and arrangement of the arm plates ; but to separate them thereby, 

 either under Cromyocrinus or otherwise, has so far proved utterly 

 impossible. It is true that the underbasals in all Russian species 

 referred to Cromyocrinus are exceptionally large, but only so in 

 the adult stage. In the young specimens, as shown by Traut- 

 schold himself, they are so minute as not to extend beyond the 

 column, so that in making the size of these plates a generic char- 

 acter we should be obliged to separate the young and adult. 



There are, moreover, several American species which in all other 

 respects agree with the typical forms of Cromyocrinus, but in 

 which these plates, even in the adult, are exceedingly small. The 

 same difficulty is met with in regard to the anal area. In two 

 species Eupachycrinus Craigii Meek and Worthen, and E. 

 Fayettensis Worthen the anal area is composed of a single plate, 

 instead of three, and this even extends partly beyond the line of 

 the radials. That this is not an abnormity, but a constant 

 character in the species, is proved by a number of specimens. In 

 every other group we should not hesitate to establish a new 

 genus on this character alone ; but in this case we are convinced 

 that it is only of specific importance, since those species agree in 

 all other respects with Meek and Worthen's typical Eupachy- 

 crinus. In one specimen of another species, in our collection, 

 only the larger, lower anal plate is absent, but this may be con- 

 sidered as abnormal, for the adjacent basal and radial plates show 

 a very irregular form. 



Examining the arms, we find them in two of the Russian species 

 of CromyocVinus composed of narrow, transverse, quadrangular 

 plates; in G. ornatus, however, they are of cuneiform pieces which 

 by degrees become interlocking plates-. The same diversity in 

 the structure of the arm plates is found among American species, 

 some interlocking almost from the base of the arm, others only 

 at the tips, while still others are constructed of a single series of 



