284 



PALEONTOLOGY OF NEW YORK. 



skirt the inner margins of the valves as a very broad, continuous lamella, 

 which is not reflexed though somewhat curved upward on the anterior margin. 



FIG. 204. 



FIG. -206. 



Fig. 205. 



Stringocephalus Burtini, Defrance. 

 Fig. 204. Urabonal cavity of the pedicle-valve with discrete deltidial plates. 

 Fig. 205. The internal sheath or projection of the pedicle-passage. 

 Fig. 206. The umbonal cavity of a pedicle-valve in which coalescence of the deltidial plates is almost complete. 



(QUENSTEDT.) 



From the inner margins of this lamellge, on its exterior and lateral extension, 

 arises a series of linear processes converging toward, and some of them perhaps 



Fig. 207. Stringocephalus Burtini. Defrance. 

 A restoration of the interior, showing the internal pedicle-sheath and the strong median septum of the pedicle- 

 valve; the great cardinal process, one of its terminal lobes (c) 1\ ing on either side of (he septum; the form of the 

 loop with the railial lilaments extending from the anterior lamellie (d) to the crura. At (a) is the insertion of the 

 diductor muscle, at (6) that ol' the adductor. (Hoernes ) 



reaching the crura. A low, thick median septum extends for about half the 

 length of the valve. 



The muscular impressions on both valves are exceedingly obscure, and have 

 never been fully described or illustrated. 



Surface smooth, with fine concentric growth-lines ; sometimes a low median 

 sinus exists on both valves near the margin. 



