BRACHIOPODA. 
31 
portion of the inner layers; and on different portions of the valves the feature 
is differently developed. In Spirifer plenus, Hall, of the Burlington limestone, 
we have an example of a true Spirifer with the apical callosity in about the 
condition of development exhibited by the Devonian species, S granulosus; that 
is, with the syringothyroid tube incipient, but in which the shell is punctated 
for its entire thickness. 
Of the Ostiolati, or syringothyroid Spirifers, the American faunas possess 
a considerable representation. The type was not specialized until the opening 
of the Devonian, and with the exception of the species just cited, S. plenus, 
and S. neglectus, Hall, of the Keokuk group, it passed into Svringothyris at the 
close of the Devonian period. It is, therefore, a Devonian spiriferoid type of 
preeminent importance. 
A member of this group which represents a form of exterior somewhat un¬ 
like that of all the other species here associated with it, is Spirifer acuminatus, 
Conrad; characterized by its broad duplicate lateral plications, a feature of the 
rarest occurrence among the Ostiolati. This specific type, however, is wide¬ 
spread, being represented in the Devonian faunas of the continent of Europe 
by the shell known as S. cultrijugatus, F. Roemer.* 
In the Upper Helderberg limestone are the following species of Ostiolati : 
S. perextensus, Meek and Worthen. 
S. macrothyris, Hall. 
(S. angustus. Hall. 
In the Hamilton group : 
S. angustus, Hall. 
S. Marciji, Hall. 
jS. acuminatus, Conrad. 
S. audaculus, Conrad. 
S. ligus—pennatus, Owen. 
S. Wortheni, Hall. 
S. Manni, Hall. 
S. acuminatus, Conrad. 
S. granulosus, Conrad. 
S.fornax, Hall. 
S. eurytines, Owen. 
S. Parry anus. Hall. 
S. asper. Hall. 
S. Macbridii, Calvin. 
* See Roemeh, Das rliein. Debergangsgebirge, pi. iv, lig. 4; Schuk., Beschr. Eifel. Bracb., pi. xxxiii, 
lig. 1. Most instructive figures are given by Quenstedt, Bi-acbiopoden, pi. lii, figs. 19-21. There is little 
doubt of the specific identity of the shells j^assing under these two names, and Robmer’s designation must 
eventually give way to the earlier one of Conrad. 
