326 
PALEONTOLOGY OF NEW YORK 
Waagen’s term for this group, Gastropegmata (or Craniacea) may therefore 
prove to be equivalent to each of these other two divisions. 
The great gulf which has seemed to exist between the Inarticulate or 
Lyopomatous, and the Articulate or Arthropomatous divisions of the Class 
Brachiopoda ; those without teeth and those with teeth; those with a largely 
corneous shell, and those whose shell is essentially calcareous, is not yet fully 
spanned at many points. 
These divisions were based upon the study of living brachiopods in which 
all the characteristic differences are pronounced and fixed. We naturally ex¬ 
pect to find, however, among the early brachiopods, in which the adjustment 
of the organism to its conditions was highly sensitive, that the oscillation and 
specialization of characters has been very rapid. The development of articulat¬ 
ing processes has already been noticed among the linguloids, in Barroisella, 
Tomasina and Trimerella, among the oboloids in Spondylobolus, and among 
the siphonotretoids in Trematobolus. It is known that the shell of many inar- 
ticulates is almost wholly calcareous, as in the Trimerellidji: and all of the so- 
termed Gastropegmata. The alteration in the nature of the shell-substance from 
protoconch, or its exemplar, Paterina, which appears to be wholly or essentially 
corneous, to the typical articulate brachiopod, in which the corneous sub¬ 
stance is reduced to a thin epidermal film, is a gradual process whose various 
stages are well understood. In Obolella, Elkania, and the early forms of Lin¬ 
gula, the deposition of calcareous salts in the shell was already advanced, these 
layers alternating with thinner layers of corneous substance. The gradual and 
eventual predominance of the calcareous shell-matter along both of these lines 
of development is seen in the ponderous Trimerellids of the later Silurian. 
The graduation of the corneous Paterina (Kutorgim Labradorica, var. Swanton- 
ensis) through Kutorgina Labradorica, and into the true calcareous Kutorginas 
{K. cingulata, it. Whitfiddi), is similar evidence. In Kutorgina Latourensis, Mat¬ 
thew described a minute tooth on either side of the pedicle-opening,* and it 
has been stated that K. cingulata shows faint traces of articulating processes at 
* Illustrations of the Fauna of the St. John Grouji, No. 3, p. 42. 1885. 
