BRACHIOPODA. 
323 
a good excuse for associating them closely, as has been done by OEhlert, who 
places the latter genus among the Inarticulates Eechwaldia presents a pecu¬ 
liar modification of the pedicle-passage, and all its essential characters, acquired 
at an early Silurian age, were maintained to the close of the Upper Silurian 
without substantial variation. The origin of Eiciiwaldia is, at present, but a 
matter of conjecture; such resemblance as it bears to Trimerella, in its incip¬ 
ient articulating apparatus, seems to be only an instance of isomorphy. 
The second main division of the Inarticulate genera is composed of those in 
which the pedicle-aperture, in the immature stages or in primitive adult condi¬ 
tions, takes the form of a marginal incision of the pedicle-valve, but becomes 
enclosed in the shell-substance in later stages of growth. To this group Waagen 
applied the term Diacaulia* (or Discinacea, 1883), which, like Mesocaulia, is an 
admirable expression of the significance of the pedicle-passage. The name 
Neotremata was subsequently introduced by Beecher (1891) as an ordinal term 
for not only such forms as these, but also for those like Crania, of whose fixation 
by means of a pedicle there is yet no evidence. 
The mode of development and enclosure of the marginal incision in the genus 
Orbiculoidea ' has already been demonstrated, f and it has been shown that 
CEhlertella, Trematis and Sciiizocrania, which have an unenclosed aperture 
at maturity, are primitive conditions through which Orbiculoidea passes in the 
development of the individual. These primitive adult conditions occur in 
various faunas from the primordial (Discinolepis) to the Lower Carboniferous 
(CEhlertella), and while these genera might be conveniently associated on the 
basis of this feature, it is doubtful whether such grouping would be a natural 
one, or a proper expression of the relations of these forms to the various con¬ 
temporary mature types. 
* This name was originally printed Daikaulia, probably a typographical error in the spelling of the 
first syllables. 
Waagen, following usage in the employment of the terms Lyopomata and Arthropomata as ordinal 
designations, subordinate only to the name of the Class, Brachiopoda, introduced Mesocadlia and Diacatjlia 
as names of suborders. It is a purely arbitrary matter whether the former terms be regarded as designa¬ 
tions of orders or subclasses. They are, in either case, inferior in the first degree to the Class itself. Hence 
the fact that Waagen emxiloyed the latter terms as suborders is no ground for rejecting either of them for a 
later name having the same significance. 
t Volume VIII, Part I, loc. cit. 
