Palcontological Speculations. — Gratacap. 79 
the theory of derivation into geological problems. 
Dr. Meyer's conclusions were based upon relationships of 
fauna, as that the lowest Claiborne is more nearly related in 
faunal features to the Jackson, than is the highest Claiborne, 
etc. ; and upon a study of variations, where it was tacitly as- 
sumed that the typical form of a species varied from its first 
characters progressively in time, giving rise to new species, 
as the original or ab-original forms disappeared.* 
Dr. Jackson in his now well known essay on the "Phylog- 
eny of the Pelecypoda'''t has engaged in the difficult labor of 
disentangling a line of descent for the Aviculidse from a hypo- 
thetical nuculoid shell and a problematic genus Rhombopteria 
which he placed in the Lower Silurian and from which 
through divergent branches of descent incorporating the 
Devonian genera Actinopteria, Ptychopteria, Pterinopecten, 
Aviculopecten, Crenipecten, Lyriopecten, Pernopecten (?), he 
reaches Pecten, Spondylus, Plicatula, Placuanomia, Placuna, 
Perna, Ostrea, Vulsella Meleagurina, Malleus. This compre- 
hensive examination of a special section was directed to the 
elucidation of a question of descent, and indicated no general- 
izations less exclusive than the origin and development of this 
group of shells. 
Also in Jackson's and Jaggar's Studies of Melonites miil- 
tipGnis, and in the former's elaborate investigation of the 
PalaeechinoideaJ the biologic processes of development and 
the morphological scheme of tesselation in the test the field of 
observation was necessarily restricted. In general treatises 
such as Gaudry'sH Les Enchainements du Monde Animal, the 
speculative conclusions of evolutional relationship are onlv 
dwelt upon in the general outlines of animal genealogy. 
In any general reference to studies of this nature. Dr. 
Beecher's essays on the Development of the Brachiopoda, 
Prof. Hyatt's work on the Phylogeny of the Cephalopoda, and 
Dr. Hall's "Hinge of Pelecypods and its Development" must 
be remembered. These are special treatises dealing, with 
•A similar mistaken inference witli regard to tlie zoological sequence 
in the Cambvian faunas, caused, for a long time, as Dr. Walcott has exnlained. 
the superposition of the olenellus beds over those carrying Paradoxides. 
■\Mem. Boxion Hoc. \af. Ilist., vol. iv.. p. 277. 
iBull. Geol Soc. America, vol. vii., l.Sa5-6, pp. 135 and 171. 
IfLes Enchainements du Monde Animal dans les Temps Geologiques ; Fos- 
•iles Priraares. 
