FOSSILS OF THE CABBONIFEKOUS. 



221 



variable, and also specifically identical with the widely distributed E. radi- 

 alis. All the specimens agree in general form, the presence of a^small 

 area and a vertically ribbed, punctate shell. In the number and strength 

 of the radiating costse, however, the greatest difference is shown. I now 

 have before me specimens with 7, 10, 12, 13, 17, 22, and 2"> costse on each 

 valve. With the two extremes to base a separation on both Eetzia Mormoni 

 Marcou, and E. radialis, var. grandicosta Davidson, appear as good species 

 one characterized by a few angular radiating ribs, and the other by numer- 

 ous rounded radiating ribs. With the intermediate links to connect the 

 shell with seven ribs and that of twenty-five and, also, any variations of 

 form that occur among many examples, we are necessitated to unite all 

 under one species,, and to refer it to Eetzia radialis of Phillips, as Davidson 

 has shown that that species has the same range of variation in the number 

 and character of the radiating ribs, and a comparison of the American 

 specimens with his figures and descriptions leaves little, if any, doubt of 

 the specific identity of the two. 



In the White Pine shales of the Upper Devonian of the White Pine 

 Mining District, Nevada, a shell occurs that is identical with the more finely- 

 ribbed examples from the Lower Carboniferous limestone of the Pancake 

 Mountains (situated between White Pine and Eureka) and those occurring 

 at relatively the same horizon near Santa Fe*, New Mexico. 



As far as our observations go, the finely-ribbed variety appears first in 

 the Upper Devonian, and the more coarsely ribbed in the Middle Carbon- 

 iferous in association with the intermediate forms, uniting them with the 

 finely-ribbed variety. 



The coarsely-ribbed variety described by Davidson, from the Punjab, 

 India, is represented by the Nevada shell bearing seven plications, and the 

 more finely-ribbed form from Russia is the usual variety from England, 

 Belgium, and America. 



Dr. Kayser has placed the specimens representing the species in China 

 under E. compressa Meek ; a variety of E. radialis Phillips. All the differ- 

 ences mentioned by Meek as characterizing E. compressa, as distinct from 

 E. punctulifera, are shown in a good series of E. radialis. 



