50 
PALAEONTOLOGY OF NEW YORK. 
by the pedicle-valve of the earlier species of Lingulops ( L . Whitfieldi, L. 
Norwoodi ). 
The brachial valve of this genus, with its little platform well defined, indi¬ 
cates a peculiar phase of accelerated development over its companion, and this 
same relation is manifested in L. Granti, which has the platforms developed in 
both valves, and also in Lingulasma, in both of which the brachial platform is 
the larger. The same feature occurs to some extent in the other genera. 
It therefore appears probable that the inception of the platform is due to the 
slight variation indicated in the mode or rate of formation of the muscular 
fulcra in Lingula, and this may itself have been due, in part, to a simple in¬ 
crease in the size of the muscular bands. 
In Lingulops Whitfieldi, the development of the platform of the brachial valve 
is not so far advanced as it appears in the other species of the genus; never¬ 
theless, its surface is divided by a longitudinal depression, its anterior edge 
distinctly elevated, and its anterior wall slightly concave. In L. Norwoodi the 
brachial platform, in its relative proportions, is almost a miniature of that in 
Trimerella, being elongated, narrow, and divided for its entire length by a 
median depression, but not hollow, though with its anterior walls more concave 
or excavated than in its congener; and in L. Granti, of the Niagara fauna, 
essentially similar characters are manifested. 
Another consideration concerning the origin of the platform is suggested by 
the chronological order of appearance of these fossils. The forms which have 
been just considered, and which indicate the line of derivation from Lingula to 
Trimerella (the latter genus being assumed to represent the climacteric develop¬ 
ment of the platform), are the predecessors of Trimerella, Monomerella and 
Rhinobolus; not remotely from a faunal standpoint, but actually, by a great lapse 
of time; the former are from the Hudson group, the latter from the Niagara 
faunas. Lingulops, strangely enough, has spanned this great interval, reappear¬ 
ing in the Niagara fauna with some important modifications, viz., the develop¬ 
ment of the muscular area of the pedicle-valve into a well-defined platform; 
possibly, also, the obliteration of the arched posterior scars. And Dinobolus, 
though attaining a culmination of development with its allies in the Niagara 
