178 NEW YORK STATE MUSEUM 



have been submitted to several accomplished morphologists, one 

 of them, Dr Robert T. Jackson of Boston, specially familiar with 

 the Echinoidea, and, while these gentlemen have kindly 

 taken time for careful examination of the various structural fea- 

 tures determinable, none have been willing to express a definite 

 opinion as to the precise taxonomic position of the fossil. To one 

 intimation from Dr Jackson however I shall take the liberty to 

 refer, as it seems to some extent borne out by the material at 

 hand. This is, in effect, that the ambulacral series 1 and 3 (see 

 accompanying diagram, plate 5) may have been continuous in 

 early stages of growth or in preexisting, more elementary types, 

 and that series 2, therefore, may have been continuous from the 

 center of the disk, thus making two series of small ambulacra, 

 each bifurcating at its extremity in the region of the periphery. 

 The suggestion, and it was intended to be no more than this, 

 would imply that the discontinuity of the ambulacral series was 

 due to the exigencies of growth, series 1 and 3 being crowded 

 asunder by the lateral growth of series 2. Such a modification 

 of structure would simplify the interpretation of the organism. 

 Among the material illustrated is a young specimen not so dis- 

 tinctly preserved as some of the larger examples, but so far as 

 it is possible to make out, these ambulacral rows do here appear 

 to be continuous radii. Perhaps the fact should be stated in 

 this way, that there is no very clear evidence of discontinuity 

 or of cycles of these ambulacral radii in this young example, 

 and so far as this specimen alone is concerned the suggestion 

 of Dr Jackson is corroborated (see plate 9, fig. 1). 



It may be well here to direct attention to a very noteworthy re- 

 semblance between this young specimen and the D i s c o p h y 1 - 

 lum pelt at um Hall, a fossil described from the " Hudson 

 river " slates at Troy N. Y., which has recently been refigured by 

 C. D. Walcott in his Mon^grapli of the fossil medusae. I can not 

 however look on the two as identical in all structural features. 



There is excellent reason for expecting from the Portage rocks 

 which have supplied these specimens of P a r o p s o n e m a, other 

 material which will retain additional details of structure sufii- 

 cient to elucidate farther the anatomy and taxonomic position of 

 this peculiar organism. 



