400 TRANS. OF THE ACAD. OF SCIENCE. 



ZEACR1NUS (continued). 



Troostanus, Meek & Worthen, 18G0. Proc. Acad. Nat. Sci. Phil., 



p. 390. — Enc. — Warren Co., Illinois. 

 Wortheni, Hall, 1858. Geol. Iowa, vol. i.,pt. 2, p. G83, fig. 111. 

 — Kask. — Chester, Illinois. 



From the foregoing Catalogue it appears that, up to the 

 present time, there have been described from the Palaeozoic 

 Eocks of the United States and Canadas seven hundred and 

 sixty-four species belonging to the class Echinodermata, af- 

 ter excluding about eighty doubtful species and varieties.* 

 These are included in one hundred and two genera and sub- 

 genera. Many of the forms now regarded as doubtful are 

 known only as catalogue names, and we may reasonably 

 expect that some of these will prove to be good species, 

 though it is well known that a large number of them have 

 been described under other names. It is also probable that 

 some of the so-called varieties will, upon careful revision, be 

 found to possess characters of full specific value. On the 

 other hand, there can be no doubt that as materials for 

 more extended examination and comparison accumulate in 

 our museums, it will appear that some of the forms now 

 recognized as distinct, are either identical with, or are mere- 

 ly varieties of, previously described species. 



Although the number of species already found in our Palaeozoic 

 strata very greatly exceeds that of all other countries combined, we 

 know that the list will be very much extended by future investiga- 

 tions. New forms are being constantly discovered, and many un- 

 d escribed species yet remain in the public and private collections 

 of the country. 



The distribution of species in the several Geological Sys- 

 tems may be stated as follows : 



In the Lower Silurian, - - 97 species. 



" Upper Silurian, - - 86 " 



« Devonian, - - - 115 " 



" Carboniferous, - - 452 " 



The following Tables show their number and distribution in 

 the subdivisions of the Systems. 



* It is a remarkable fact that a single locality in the Encrinital Lime- 

 stone, occupying but a few acres in extent— Burlington, Iowa— -has yield- 

 ed 261 species, or more than one-third of the entire number described from 

 our Palaeozoic rocks. From another locality, a few yards square, in Gray- 

 son County, Kentucky, the writer has collected in a few minutes upwards- 

 of 150 good examples of the cup of Zeacrinus crateriformis . 



