BRACHIOPODA. 
49 
S. disjundus. These observations have not yet been verified, but it would be 
reasonable to expect such phenomena even among Spirifers not belonging to 
the group of Ostiolati. Yet here, as in so many other generic groups of the 
brachiopods, it is the extreme development of a given peculiarity which serves 
as a basis of generic distinction from forms possessing the same character in a 
state of incipiency. 
What may have been the function of this organ in the physiology of the 
animal is still a subject for speculation. King suggested that it might have 
been a base of attachment for the pedicle-muscles. The pedicle, however, was 
probably atrophied in the mature condition of these shells; at least all means 
of egress were obstructed, except beneath the deltidium. There is no reason 
from analogy for assuming that the pedicle ever passed through this aperture 
but in case it was thus extruded. Dr. King’s supposition seems a plausible one. 
If, however, the pedicle was atrophied from the closure of its normal channel 
nearer the beak, this calcareous tulie may have been an exudation encysting 
this functionless organ. In one interesting species from the earliest of the 
Carboniferous faunas, S. Herricki, Schuchert, there is a solid process in place 
of a tube beneath the transverse plate, which is extended to the bottom 
of the valve, thus forming a septum supporting the transverse plate, and 
exhibitino; in a striking manner an inclination toward the internal structure of 
Spiriferina. 
The divergent views of King and Carpenter in regard to the punctation of 
the shell in cuapidatus are well known, and the discussions may be found 
principally in the Annals and Magazine of Natural History, and the Geological 
Magazine for the years 1867 and 1868.* 
The late F B. Meek was the first to demonstratef that the shell substance 
in S. cuspidatus is punctate, and probably all the species possessed of a transverse 
plate and split tube have this shell structure. This punctation has been de¬ 
scribed as “ patchy; ” it is better developed or better retained in some parts of 
* The student may also be i-eferred to Dr. Carpenter’s earlier observations in his report to the British 
Association, 1844, “On the Microscopic Structure of Shells,” and to his ti-eatise in Davidson’s Introduction, 
“ On the Intimate Structure of the Shells of the Bi-achiopoda,” 1852. 
t Proc. Academy of Natural Sciences, Phila., vol. ix, second ser., p. 275. 1865. 
