54 
PALAEONTOLOGY OF NEW YORK. 
depression of the surrounding surface of the shell is never so marked; the 
platform itself is of less size throughout, and we have noticed that in the course 
of its development it does not make its appearance so early as in the brachial 
valve. The lead held by the brachial valve in this respect, as sjhown in Ltngu- 
lops and Elkania, is maintained throughout the entire history of the organ. 
The cause of this is not far to seek. In Lingula, the anterior portion of the 
visceral region lying directly in front of, and 
behind the insertion of the anterior muscular 
bands, is occupied by the liver. In L. anatina, 
rather the greater portion of this body lies 
behind these muscular scars, but in Lingulops 
there is a general posterior concentration of all 
these muscular bands. In such a case the retro¬ 
gression of the muscles could not force the liver 
into a more contracted space or otherwise 
displace it than to change its relative position 
and leave the large muscular bands behind it. 
This organ (the liver) is large, and lies mostly 
on the dorsal aspect of the animal, the surface 
there covered by it, in L. anatina, being con¬ 
siderably more extensive than on the opposite 
side. It is also distinctly bilobed by the longi¬ 
tudinal septum on the brachial valve. The 
pressure of this organ against the anterior edges 
of the area of muscular implantation must have been of significance in induc¬ 
ing the formation of the anterior elevated margins of the muscular scars, and 
in this pressure, continued as a constant force in both valves, though less in¬ 
tensely in one than in the other, may, perhaps, be found an efficient cause for 
the abrupt termination of the muscular area, its elevation, its concave anterior 
walls, and, eventually, its complete excavation, as well as the depression of the 
adjoining surfaces of the shell. 
In discussing the genus Dinobolus, attention has been directed to the tendency 
ml of the 
Fig. 17. Lingula anatina 
AL oral aspect, showing the arrangi 
riscera on the inner surface of the brachial 
•alve (after King). 
h, central scars. a, liver. 
j, anterior lateral b, genitalia. 
scars. e, alimentary canal. 
