142 The American Geologist. March, isos 
objects, :is in Crania. The first section is again divided into three 
groups, on the basis of the position of the pedicle, (a) pedicle 
emerging from between the valves, as in Lingula, {/>) ventral 
valve perforated for the protrusion of the pedicle, and (c) unce- 
mented shells without a pedicle opening. The third group, how- 
ever, is identical with h, since Lrptiena, Fmductxs and Stropho- 
mrna, genera referred to section r, do possess a pedicle opening. 
While this classification lacks a complete understanding of the 
features in question, it is remarkable that VonBuch, nearly sixty 
years ago, and Deslongchamps,*'' twenty-eight years later, recognized 
some of the principles upon which the classification of the Brach- 
iopoda is now ])eing established, viz. : the nature of the pedicle 
opening. 
Up to 1846 the general external features of brachiopods served 
the majority of authors as the essential basis for generic diflfer- 
entiation. In that year, ' however, King'^ pointed out that more 
fundamental and constant characters exist in the interior of the 
shell, a fact which soon came to be generall}^ recognized, mainly 
through the voluminous writings of Thomas Davidson. 
In 1848, Gray,* probably stimulated b}' King's' paper, divided 
the Brachiopoda into two sub-classes, Ancylopoda and Helirto- 
p>o<la. These divisions rest entirely on the basis of the arm struct- 
ure and the presence or absence of a calcareous support. The 
Ancylopoda are distinguished in having the "oral arms recurved 
and affixed to fixed appendages on the disk of the ventral [dorsal] 
valve," while in HiUvtopoda '-they are regularly spirally twisted 
when at rest. " The brachia, however, in all recent species, are 
recurved and more or less spirally enrolled, except in some gera- 
tologous forms of loop-bearing genera, as Cistrlla and Girynia. 
Therefore Helicfopoda, as far as the arm structure is concerned, 
will also include the Ancylopnda. In fact, to the former he 
referred only the terebratuloids, if Thfcidium is excluded, while 
Ancylopoda contained all other brachiopods whether articulate or 
inarticulate forms. These sub-classes are further divided, on the 
basis of the brachia, into four orders, Anrylohrarhia, Crypto- 
hrac/iid, ScJrrohnnhia. and Sarcicobraclna. Of these the first 
only can be retained as a sub-order, since it includes the loop- 
hearing genera. The other orders have so heterogeneous an as- 
semblage of forms as to be of no permanent value. 
Beyond the introduction «)'" ;u'\v families, no further attempt 
