4 
PALEONTOLOGY OF NEW YORK. 
Diagnosis. Shells sub-equivalve, equilateral; elongate-ovate, sub-quadrate 
or sub-triangular in outline; broad over the pallial region, cardinal slopes more 
or less conspicuous; slightly gaping at both extremities. Brachial or dorsal 
valve somewhat the shorter, and with a slightly thickened hinge-line. Surface 
of the shell smooth, or concentrically and radiately striated. Animal attached 
by a long, muscular pedicle protruding from between the beaks of the two 
valves. 
Muscular impressions numerous, but usually in¬ 
distinct. In the recent species they are twelve 
in number upon each valve, and are somewhat 
unsymmetrical in their arrangement. They may 
be designated as follows: The umbonal impressions 
(g), produced by a single muscular band passing 
directly across the cavity of the shell near the 
beaks, and by their contraction opening the valves; 
the lateral impressions, which are produced by 
three pairs of muscles, the anteriors (j) passing 
from near the lateral boundaries of the visceral 
area on the pedicle-valve, forward to the anterior 
extremity of this tract on the brachial valve; the 
middles ( k ) passing in just the opposite direction, 
from the anterior region of the pedicle-valve to 
the lateral region of the brachial; the externals 
(l) passing from the ante-lateral region of the 
pedicle-valve to the post-lateral region of the 
brachial valve, these muscles serving to move the 
valves forward and backward. The central impres¬ 
sions ( h ) are produced by a single pair of muscles extending across the ante- 
lateral region of the visceral area, and by the contraction of these, the valves are 
closed. The transmedian impressions (i), are made by a triple muscle, one band 
of which is on one side the visceral area, the other two on the other side, the 
two lateral components crossing each other in passing from the posterior region 
ig. 1. Lingula anatina , after Hancock. 
p , pedicle ; g , umbonal muscle; h , cen¬ 
trals ; i, transmedians; j , 7c, l , laterals ( j , 
anteriors, k , middles, l , externals); e , heart; 
o,mouth; a , alimentary canal; z , anus. 
