308 



PALEONTOLOGY OF NEW YORK.\ 



short, triangular plate or diaphragm which begins at the apex of this valve, and 

 extends forward beyond the posterior edge of the brachial valve, and thus serves 

 the purpose of the deltidium, though deeply depressed within the cavity of the 

 pedicle-valve. This diaphragm is usually quite short and confined to the apical 

 region, but it may extend for fully one-fifth the length of the valve, its anterior 

 margin being free and its lateral margins adherent to the inner cardinal slopes. 

 The cardinal line may be regarded as extending nearly to the lateral ex- 

 tremities of the valves ; the articulating apparatus consists of a pair of long 

 marginal ridge-like teeth on the divergent cardinal slopes, fitting into narrow 

 marginal grooves on the brachial valve. There is sometimes a trace of a 

 median septum over the pallial region. In the brachial valve is a small callus, 

 boss or cardinal process lying directly beneath the apex. Below this is a strong 



Fio. 229. 



Fig. 231. 





Fio. 232. 



Fio. 233. 



Eichwaldia reticulata,' Hall. 



Fio. 280. 



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{/m^^y 



FIO. 2.15. 



Fig. 233. Interior of brachial valve. 

 Fig. t34. Vertical section of shell. 

 Fig. 285. Enlargement of tlic surface. 



Fig. 229. Doraal view. 

 Fig. 230. Cardinal view. 



Fig. 231. Longitudinal section of the two valves. 

 Fig. 232. Interior of pedicle-valve. 

 Notaiion i t, " bare spot," foramen ? ; p(o), deltidlain or internal plate; c', umbonal surface of pedioie-valve; T, teeth; 

 B, dental sockets; j, cardinal process; 8, median septum of brachial valve. 



median septum, which increases in height anteriorly and rises to an acute, an- 

 teriorly directed apex at about two-thirds the length of the shell. In front of 



