202 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



the low fold and strong lateral plications throughout its entire life history. 

 Index curves and the characters common to both and their common order of 

 appearance suggest a common origin, and P. suMaticosta occupies the right 

 stratigraphic position and has all the characters necessary to be an ancestor 

 of these two species. 



The Secretary next presented a discussion on American Silurian 

 ostracoda for the author. Illustrated by specimens and lantern slides; 

 discussed by Messrs. Grabau, Schuchert, Ulrich, and Bassler. 



THE OSTRACODA AS GUIDE FOSSILS IN THE SILURIAN DEPOSITS OF THE 

 APPALACHIAN REGION 



BY E. 0. ULRICH 



(Abstract) 



The exact time relations of the Silurian deposits of the Appalachian Valley 

 with respect to the standard section of the interior of the continent have long 

 bfeen conjectural, but it has always been recognized that the ostracoda, on 

 account of their exceeding abundance and excellent preservation, would seem 

 better for correlation than almost any other group of fossils. Another reason 

 for the use of this group in correlation is that the same species will occur 

 indiscriminately in limestone, shale, or sandstone, and so well preserved in 

 each case that exact determinations are possible. Even when preserved as 

 molds in sandstone a gutta-percha squeeze will give all the essential features 

 of the carapace. 



Hitherto less than half a dozen Appalachian Silurian ostracoda have been 

 recognized, but as a result of the present work no less than twenty-seven new 

 genera and several hundred species are known. An interesting feature has 

 been the discovery that species and genera otherwise quite similar can readily 

 be distinguished by the form and position of the swelling on one of the lobes 

 of certain individuals which are considered the female forms. On the assump- 

 tion that this swelling is the brood pouch, the long controversy as to which is 

 the anterior and posterior end of these Paleozoic ostracoda can now be settled, 

 since the swelling always marks the posterior end of the carapace. 



R7<]P0RT OF THE ATJDITIN-G COMMITTEE 



At this point the Auditing Committee gave notice that their report on 

 the accounts of the Treasurer was ready. The correctness of the accounts 

 was attested by the committee and the Society voted that their report be 

 accepted. 



The reading of papers was then resumed with the presentation of the 

 following, which was illustrated by lantern slides. Discussed by Messrs. 

 Mook, Schuchert; and Twenhofel. 



