BRACHIOPODA. 



331 



Figs. 28-30. Murginifera typica, Waagcn. 

 After Wa.^gen. 



The peculiar features described may perhaps be valid ground for the 

 proposed subdivision when in their extreme development, as in M. 

 typica and M. ornata, Waagen (see figures in the work cited, plates Ixxvi and 

 Ixxvii), but an examination of extensive collections shows that these 

 elements appear, in various stages of development, in different species, from 

 the middle Devonian upward through the Coal Measures. In all the Amer- 

 ican species examined, the characters on which this division is founded seem 

 to be rather in an inceptive condition when compared with Marginifera typica, 

 and can scarcely be considered as of such organic importance as to warrant the 

 generic separation of such forms, especially when it will involve a considerable 

 number of species in which the articulating apparatus and all the more essential 

 characteristics correspond with Productus. Unless applied in a very restricted 

 sense, this term can scarcely be adopted to designate an altogether reliable 

 separation from Productus, for it is manifest that many species, possessing 

 incipient internal characters which show them to be in the line of develop- 

 ment toward Marginifera can not, on such grounds, be separated from the old 

 genus, while the number of forms in which these characters described become 

 fixed and highly developed, are very few. 



