162 



PALEONTOLOGY OF NEW YORK. 



margin of l)otli valve.s modified I'or tlie passage of the pedicle l>et\veen 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. 



fi. llinj;c'-l('i-th i<\' lii':u'lii;il v;il\c. 



h. Hinge-tfulh cil' iii;<liclt'-v.-ilve. 



f. Spniich'cular i)latc of br;tclii;il 



valve. 



ft. Median tentacle. 



/. Parietal bands. 



ff. Body oavit\'. 



h lAvcv. 



k- Hepatic clianiber of .-stomach. 



I. Intestinal cliaml>er of .stomach. 



m. Intestine. 



n. Anus, 



o. Mouth. 



p. Muscles (priinai-y). 



q. l.ophophore. 



r. Posterior unpaired nniscle. 



V. Pallial sinus. 



in Its opening into the bo'ly cavity 



Kmbryonic >tage.s of Liiujida iiiiramhiiita, .Siimpson {,— (JluttUlui Amhliiii-li, Brodcrip). 



After BuooKS. 

 Fi<i. ".'). Dorsal view of the youngest larva observed. X 250. 

 Fio. 76. Dorsal view of a somewhat older embryo. X '-5". 

 Fig. 77. Ventral view of an individual soon after beoondng sedenlary. ii» indicate^ the cilge of I he larval shell. 



The eml)ryological history of Lingula, as elaborated by Brooks,* for L. 

 pijramidata {=^ 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 



Ohesapoake Zoological Lahoi'atory ; Scientific Ileault.s of Ses.sion of 1S7S. 



