336 
PALEONTOLOGY OF NEW YORK. 
The cardinal area is a feature more generally developed among the forms in¬ 
cluded by Waagen under his term Aphaneropegmata (=Protremata, Beecher), 
that is, among forms possessing the deltidium, but it is very irregular in its occur¬ 
rence among all the articulate Brachiopoda. The genus Spirifer furnishes a 
most striking instance of its persistence in the deltarium-bearing shells ; its usual 
absence in Pentamerus and Conchiuium serves to demonstrate that it is not an 
indispensable character of its group. It is probable that the existence of this 
area has little fundamental connexion with the condition of the pedicle-passage. 
It is a very palpable fact that there is a much more intimate relation 
between it and the general form of the shell; thus in the elongate shells, like 
the terebratuloids, meristoids, retzioids and the pentameroids for the most part, 
there is no such area present. Where the form of the shell is more generally 
transverse, as among the Orthid^, in Strophomena, Clitambonites, Derbya, 
Spirifer, etc., the area is highly developed. This area is a characteristic 
feature of all early deltidium-bearing species, and, where it manifests itself 
occasionally in one of these groups which has for the most part lost, or never 
developed this area, as in Porambonites, Gypidula and Pentamerella among 
the pentameroids, its appearance may be regarded as the resumption of a 
primitive or original character which was normal for that division of the 
Articulates in some period of its history. 
Similarly we meet with a cardinal area in an early rhynchonellid type, 
Orthorhynchula, and this is an evidence of the first significance as indicating 
the source from which the extensive group of the Rhynchonellas originated. 
These are shells which, at a very early period, assumed the deltarium or sec¬ 
ondary condition of the pedicle-covering. It would be presumptuous to assume 
that a single species of this great group developed a cardinal area solely from 
mechanical causes, such as obstructed growth on the posterior margins of the 
valves. Its presence seems, rather, to suggest the perpetuation of an ancestral 
character indicating that these modified shells have been derived from a more 
primitive condition in which the cardinal area was normal and, no doubt, 
accompanied by a deltidium. In the absence of further evidence such a char¬ 
acter is of much interest and importance. 
