162 



PALEONTOLOGY 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 peilicle-valve. 



c. Semicircular plate of brachial 



valve. 



Median tentacle. 



Parietal bands. 



Body cavity. 



Liver. 



Hepatic chamber of btomach. 



Intestinal chamber of stomach. 



Intesline. 



Anus. 



Mouth. 



Muscles (primary). 

 q. Lophopliore. 

 r. Postei'ior unpaired muscle. 

 V. Pallial sinus. 

 w. Its opening into the body cavit.v. 



d. 

 /. 

 0- 

 ft. 

 ft. 

 I. 



V 



Embryonic Stages of Lingula pyramidata, Stimpson (= Glotiidia Audcburti, Broderip). 



After Brooks. 

 Fig. 75. Dorsal view of the youngest larva observed. X 250. 

 Fio. 76. Dorsal view of a somewhat older embryo. X '-50. 

 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 two 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 /, 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. 



