A KEVISION OF THE PALAEOZOIC PALAEECHINOI- 

 DEA, WITH A SYNOPSIS OF ALL KNOWN SPECIES.* 



Mary J. Klem. 



Among the Echinodermata, the Palaeozoic Echini present 

 a most fertile field for the study of variations and abnormal 

 development, — features which are common, however, 

 throughout the sub-kingdom. Having had at my command 

 for study a very large and excellent collection, I wish to offer 

 a few suggestions as to the probable development of these in- 

 teresting fossils. 



I take this opportunity to express my sincere thanks to my 

 dear friend and teacher, Dr. Hambach, professor at Washing- 

 ton University, for the use of his valuable collection and 

 library, as well as for the interest he has taken in the prepa- 

 ration of this paper. All the drawings submitted were made 

 from specimens in the Doctor's collection, and most of the 

 works quoted are in his library. 



Before entering upon the detailed study of the development 

 and arrangement of the different parts, it may be well to note 

 the classification of fossil Echini. All the Palaeozoic Echini 

 belong to the class Oidaridae, and differ from the Mesozoic, 

 Cenozoic and living species, in having never less thanfour rows 

 of plates in each interambulacrum, with the exception of one 

 order, Bothriocidaroida. They may be conveniently divided 

 into three orders: (1) Cystocidaroida with four rows of 

 plates in the ambulacrum and numerous rows in the inter- 

 ambulacrum; (2) Bothriocidaroida with two rows of plates in 

 each ambulacrum and one row in each interambulacrum; (3) 

 Perischo'echinoida with never less than two rows in each am- 

 bulacral area and never less than four rows in each interambu- 

 lacral area. 



In the following discussion I shall confine my attention 

 chiefly to the Melonitidae , a family of the Perischo'echinoida. 



* Fresenied by title to The Academy of Science of St. Louis, Jan., 1904. 



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