162 
PALAEONTOLOGY OF NEW YORK. 
margin of both valves modified for the passage of the pedicle between them, 
may take a position near the base of the system, and its elaborate muscular 
apparatus may establish it in such a position as a comprehensive type or point 
of departure for many derivatives. 
a. Hinge-teeth of brachial valve. 
b. Hinge-teeth of pedicle-valve. 
c. Semicircular plate of brachial 
valve. 
d. Median.tentacle. 
/. Parietal bands. 
g. Body cavity. 
h. Liver. 
lc. Hepatic chamber of stomach. 
1. Intestinal chamber of stomach. 
o. Mouth. 
p. Muscles (primary). 
q. Lophophore. 
r. Posterior unpaired muscle. 
v. Pallial sinus. 
w Its opening into the body cavity. 
Embryonic Stages of Lingula pyramidata, Stimpson (r= Glottidia Audebarti, Broderip). 
' After Bhooks. 
Fig. 75. Dorsal view of the youngest larva observed. X 250. 
Fig. 76. Dorsal view of a somewhat older embryo. X 250. 
Fig. 77. Ventral view of an individual soon after becoming sedentary, nu indicates the edge of the larval shell. 
The embryological history of Lingula, as elaborated by Brooks,* for L. 
pyramidata (= Glottidia Audebarti ), has an important bearing upon the taxonomic 
position of this group. The author has shown that the shell in its earlier stages, 
has a subcircular form, and that the posterior opening for the pedicle is as fully 
developed on one valve as on the other; further, that the muscular bands first 
to appear are a great posterior or umbonal, and tv^o simple transverse bands 
crossing the interior cavity (but not each other) near the oesophagus. The lat¬ 
ter are regarded by Brooks as representing the muscles h, j, k and l, of the 
mature animal (see figs. 6, 7, page 10). All these features are apparent in 
shells of the obolelloids; the subcircular valves, the pedicle-passage, sometimes 
Chesapeake Zoological Laboratory ; Scientific Results of Session of 1878. 
