213 
PALEONTOLOGY OF NEW YORK. 
together with 0. platys, Billings, from the Chazy, 0. Saffordi, sp. nov., and 
probably O. Holstoni, Safford, from the Trenton, form a small group distin¬ 
guished by its peculiar exterior, though the internal characters of the species 
are still undetermined. To establish the true generic value of all these forms 
will require much patient work both in the field and in the laboratory. 
The orthids occurring in primordial faunas have in so many instances shown 
a comprehensive structure, having characters which individually are distinctive 
of Orthis, Orthothetes, Clitambonites, Scenidium, etc., that it may be ques¬ 
tioned whether any of these primordial forms can be included under Orthis 
according to the strict definition of the term, or even under any of the sub¬ 
divisions here proposed. 
The development of the punctated shell-structure in this genus is a peculiar 
phenomenon.* In eight of the thirteen proposed subdivisions of Orthis, the 
shell-structure is prismatic but impunctate. So far as now known there is not 
an impunctate Orthis in the faunas later than the Silurian. On the other hand 
the punctate species are decidedly in the minority in Silurian faunas, attaining 
their great numerical development in the Devonian. The first appearance of 
punctation is along the line of the O. testudinaria group (Dalmanella), but evi¬ 
dence is still required to show that some of the earliest species included in this 
* Thin sections of these shells have been made whenever material has been favorably preserved or in 
sufficient quantity to allow it, and no evidence has been found of an indiscriminate or sporadic appearance 
of this punctation, though it has, naturally, been impossible to study the shell-structure in every species 
examined. It was originally a part of the plan and purpose of this work to take up the study of the minute 
shell-structure in connection with the generic studies, and to include the result of the investigation in this 
volume, as a part of the contribution to our knowledge of the Palaeozoic Brachiopoda. The lapse of nearly 
twenty years from the commencement of this work till it was again taken up, in 1888,f has brought much 
new material for consideration, while the studies and publications of numerous authors have served to 
present the subject in new aspects, and at the same time to demand a somewhat different treatment from 
that originally contemplated. Owing to these conditions the study of the shell-structure has been postponed 
for the present, but it is the ultimate purpose of the author to take up as a special subject the examination 
of the minute shell-structure in the different genera of Palaeozoic Brachiopoda. 
t The work of a revision of the genera of the Palaeozoic Brachiopoda was begun soon after the completion and pub¬ 
lication of Volume IV of the Palaeontology of New York, and thirty plates, beginning with illustrations of the generic 
group of Orthis had already been lithographed, from drawings chiefly made by Mr. ft. P. Whitfield, when it became 
necessary to suspend the work. These plates, originally numbered from aV to XXXVI, were mostly lithographed by Mr. 
PHiLir Ast; two of them by Swinton, two by Riemann and two by Bergman, between the years 1870 and 1876. Of 
these plates aV and V have been cancelled, and, with large additional material and accumulated information, have been 
substituted by V, Va, Vb, Vc. The original plates, from VI to XIX, are included in this volume, and are supplemented by 
VIA, VIIa, XIa, XIb, XIC, XId, XVa, XX. 
