BRACHIOPODA. 
331 
Figs. 28-30. Marginifera typica, Waagen. 
After Waagen. 
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 lxxvi and 
lxxvii), 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. 
