MOLLUSCA. 659 



fully compared with the recently collected examples which are 

 here referred to T. irregularis, and there can be no doubt as to 

 their specific identity; it also is without doubt a Merchantville 

 clay-marl specimen, and it is safe to conclude that it is a synonym 

 of T. irregularis. 



Formation and locality. Merchantville clay-marl, near Ma- 

 tawan (101), Lenola (163). 



Geographic distribution. New Jersey, Arkansas. 



Teredo species undertermined. 



At Mullica Hill some Teredo-likt borings in a fragment of 

 wood have been observed, which strongly resemble T. irregu- 

 laris, and from the tubes alone might be so identified. They 

 seem to be somewhat straighter, however, than the typical forms 

 of T. irregularis from the Merchantville clay-marl, and in the 

 absence of any knowledge of the shell which inhabits them, it 

 is not possible to identify them with certainty. In the Marshall- 

 town clay-marl Teredo-like burrows have been observed which 

 are even more like those of T. irregularis, but the shell inhabiting 

 them is quite different from that species, and it is therefore more 

 than probable that these Navesink specimens belong to another 

 .species. 



Formation and locality. Navesink marl, Mullica Hill (169). 



Geographic distribution. New Jersey. 



Genus POLORTHUS Gabb. 



Polorthus tibialis (Morton). 

 Plate LXXIV., Figs. 12-15. 



1834. Teredo tibialis Mort, Synop. Org. Rem. Cret. Gr. U. $., 



p. 68, pi. 9, fig. 2. 

 1 86 1. Teredo tibialis Gabb, Synop. Moll. Cret. Form., p. 230 



(174). 



1861. Polorthus tibialis Gabb, Proc. Acad. Nat. Sci. Phil. 

 (1861), p. 366. 



