12 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



from the Cincinnatic formations; while the Wachsmuth material has 

 species from the Mississippic. To all of this material the author 

 has had access through the kindness of Director Samuel Henshaw 

 and Profs. R. T. Jackson and P. E. Raymond. 



At the University of Chicago there is a great deal of excellent 

 material in the W. F. E. Gurley, Charles Faber, and U. P. James 

 collections, to which Weller has added other specimens. All of this 

 material has been studied through the courtesy of Prof. Stuart 

 Weller. Most of it is from the Cincinnatic formations. 



All of the specimens described by E. Billings and now in the Vic- 

 toria Memorial Museum in Ottawa, Canada, have been seen at one 

 tune or another. In this matter the writer was much aided by the 

 late Dr. J. F. Whiteaves and more recently by Drs. P. E, Raymond 

 and E. M. Kindle, to the latter of whom thanks are also due for 

 several photographs reproduced in this memoir. Most of the speci- 

 mens are from the Ordovicic. 



In the University of Toronto there is much material from the 

 Ordovicic and Siluric in the Sir Edmund Walker collection, and there 

 may be studied a great many specimens of Stenaster salteri. All of 

 this has been seen through the great liberality of Prof. William A. 

 Parks. 



The genotype of Pakeaster, from the museum of Cornell University, 

 was loaned to the author at different times by Prof. H. S. Williams. 

 It is one of the best preserved of Paleozoic specimens and has become 

 very valuable because of the continual discussion that centers 

 around the species, P. niagarensis. 



To all the specimens in the Peabody Museum of Yale University 

 access was had through the kindness of the late Prof. Charles E. 

 Beecher. Among them is the unique branching form, Eucladia 

 beecfieri. 



Photographs have been made for this memoir by Dr. John M. 

 Clarke of specimens in the New York State Museum, and by Prof. 

 George H. Hudson, of Plattsburg, New York, of other material. 

 Prof. Arthur M. Miller loaned two specimens that he collected and 

 deposited in the State University, Lexington, Kentucky. Prof. George 

 W. Harper, of Cincinnati, loaned a specimen of Palseaster darkana 

 ( = Hudsonaster incomptus) . 



Nearly all the original drawings were traced from the specimens 

 by aid of the camera lucida. These outlines were then inked and 

 shaded by the late Dr. J. C. McConnell, a draftsman and artist of 

 the first rank. 



To Miss Clara Mae LeVene the writer is especially thankful for 

 the great interest she has taken hi getting the manuscript into order 

 for the printer, keeping the bibliography up to date and correctly 

 citing it, and for the careful reading of the proof. 



