BRACHIOPODA. 
53 
Fig. 42. 
Spiriferina Walcotti,^ovio» \>y \ showing mus¬ 
cular scars on walls of median septum of 
pedicle-valve, (c.) 
The accompanying figure of S. Walcotti, Sow- 
erby, shows the great elevation of this wall, and 
the broad scars of the adductor muscles upon its 
lateral faces. This specimen indicates how im¬ 
portant are the changes in the anatomy of the 
animal, resulting from, or productive of this 
median septum. The older species have furnished 
no direct evidence of similar muscular attach¬ 
ment, but there is no reason for doubting its 
existence wherever such a septum is found. 
As far as observed, the loop of the palaeozoic species is slightly different from 
that of the later members of the genus, and resembles that of Cyrtina, the 
lateral portions converging upward, between the spiral coils, and uniting in a 
slight anterior extension. The spiral ribbon is spiniferous in S. rostrata, but 
usually smooth in the Carboniferous species. In S. spinosa, and probably in 
other species, there is a solid calcareous deposition in the umbonal cavity of 
the pedicle-valve, filling the interspaces between the dental lamellae and the 
median septum, not constituting a union of the three plates as in Cyrtina, but 
forming a secretion analogous to that found in the syringothyroid Spirifers, 
and to the transverse plate in Syringothyris itself. Both the palaeozoic and 
Liassic species have broad crura, a faint elevated median ridge in the brachial 
valve, and a pair of divergent ridges lying on the surface of the first 
internal plications, extending fully, or more than one-half the length of the 
valve, and ending abruptly; probably the external fulcra of the adductor 
muscles. 
It has already been observed that the derivation of the generic characters of 
this genus has been from the lamellose-septate Spirifers whose inception dates 
from the faunas of the Upper Silurian. Though none of these Silurian and 
Devonian species, in the American faunas, developed a punctate shell structure, 
they usually bear the lamellose, often radially striated exterior, prevailing 
among the Spiriferinas of the Carboniferous. Mr. Davidson has described two 
of these lamellose species from the Devonian, which have a strongly punctated 
