314 STUDIES IN EVOLUTION 



of the minor deductions may not apply, in every case, to 

 the individuals of the same species found in other regions. 

 The writers have also refrained, except when essential to the 

 proper exposition of a species, from entering into details of 

 synonymy or generic controversy as to the correct reference 

 of the species. This course is considered advisable, from a 

 desire not to introduce any discussions alien to the descrip- 

 tions of the developmental changes in these organisms. Aside 

 from this it is believed that a number of important facts are 

 here added to the knowledge of the Brachiopoda, and that 

 many of them will be found to be of general application. 

 The investigation has also resulted in elucidating several 

 obscure and anomalous features of the shell and of the cardi- 

 nal area, which appear in their proper place in the description 

 of the species and in the general summary. 



The following list includes all the species of Brachiopoda 

 which up to this time have been described from the shales 

 at Waldron, Indiana, and comprises forty-two species and 

 varieties, ascribed to twenty-four genera. It also shows 

 whether material has been obtained which furnishes data for 

 tracing the developmental changes. 



The majority of the species which have afforded no young 

 specimens are rare forms even in their adult state. Among 

 the actually abundant species of which there are no means 

 accessible of tracing the life-history, Uncinulus Stricklandi is 

 a noticeable example, and it is really the only common species 

 which has afforded no young shells. Meristina Maria, another 

 abundant form, furnishes a series which is notably incomplete, 

 as the youngest individual observed, which can with certainty 

 be referred to it, has a length of 6 mm. Likewise the inarticu- 

 late species have yielded almost no immature specimens. 



List of the Brachiopoda occurring in the Niagara Shales at 

 Waldron, Indiana. 



Crania siluriana Hall One embryo. 



Crania setifera Hall No young shells obtained. 



Crania spinigera Hall " " " 



