108 
PALEONTOLOGY OF NEW YORK. 
that the generic characters are not only very distinctly defined, but are of such 
a nature as to remove all these forms widely from Obolella and its immediate 
allies. This is seen in the character of the muscular impressions alone; the 
absence of the great lateral scars, the broad, composite centrals, and the deep 
pedicle-pit of the ventral valve, all of which are indicial features of the obolel- 
loid genera ; furthermore there is no evidence of any cardinal area or anything 
more than a somewhat flattened margin of 
contact in either valve. On the other hand 
there are present (in L. sagittalis) conspicuous 
cardinal scars in each valve, of similar char¬ 
acter to the posterior adductors of Crania (as 
suggested by Mr. Davidson, loC. cit., p. 340), FIG. 60 . Internal cast of U pe°cUcle-valvel 
r . Fig. 61. Internal cast of brachial valve. 
which, in L. transversa and L. msera, take 
the form of stout tubercles or bosses, situated just within the posterior margin; 
and a mammiform or subtrihedral apical tubercle, which is perforated by a 
minute foramen (see Plate III, figs. 35, 37-39, 43). This feature was not 
represented in Mr. Davidson’s figures of Obolella sagittalis, but was first pointed 
out by Linnarsson {loc. cit.), and is clearly seen in well preserved specimens. 
The character of the pedicle-aperture is of itself of sufficient significance to 
remove these species from the vicinity of Obolus and Obolella, where this 
opening is always a groove on a well defined cardinal area, and to endorse its 
association with Acrotreta, Acrothele, Schizambon, and the other allies of 
Siphonotreta. The posterior submarginal tubercles or bosses have undoubtedly 
served as fulcra, probably of the adjustor rather than of the adductor muscles, 
acting to keep the valves in place, and they may be compared to the articular 
bosses in the genera Spondylobolus and Barroisella. 
The brachial valve has a less conspicuous development of these tubercles, but 
they are distinctly seen in L. transversa, L. sagittalis and L. Taconica. Between 
them lies a strong axial septum, which is broadened over the central portion 
of the shell, and is accompanied for most of its length by a shorter and narrower 
ridge on either side, from each of which it is separated by a sharp furrow. 
The substance of the shell, in all the specimens which have passed under our 
