656 CRETACEOUS PAIvEONTOLOGY. 



ters, but a comparison with Gabb's type of M. cretacea has shown 

 them tQi be not essentially different from that species. Some of 

 the examples are shorter than usual and consequently taper more 

 abruptly to^ the posterior extremity than the average form, but 

 the most important variation is the presence or absence of the 

 supplementary oblique furrow in front of the primary one ex- 

 tending from the beak toi the ventral margin. In the majority 

 of individuals this .furrow is present and its absence is more apt 

 to be a feature O'f the smaller and presumably younger shells. In 

 a few specimens oi nearly maximum size this furrow is nearly 

 obsolete, being noticeable only near the ventral margin, and in 

 one specimen it is absent from one valve although faintly indi- 

 cated on the other. 



Formation and locality. — 'Merchantville clay-marl, Lenola 

 (163); Marshalltown clay-marl, near Swedesboro (177). 



Geographic distribution.- — New Jersey. 



Family TERBDINIDAE. 



Genus TerEdo Ivinneus. 

 Teredo irregularis Gabb. 

 Plate LXXIV., Figs. 1-3. 



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



p. 68 (in part). 

 1060. Teredo irregulcwis Gabb, Jour. Acad. Nat. Sci. Phil., 2nd 



sen, vol. 4, p. 393, pi. 68, fyg. 19. 

 1861. Teredo contorta Gabb, Proc. Acad. Nat. Sci. Phil. 



(1861), p. 323. 

 1861. Teredo irregularis Gabb, Synop. Moll. Cret. Form., p. 



230 (174). 

 1864. Teredo contorta Meek, Check List Inv. Eoss. N. A., Cret. 



and Jur., p. 16. 

 1864. Teredo irregularis Meek, Check List Inv. Fobs. N. A., 



Cret. and Jur., p. 16. 

 1868. Teredo contorta Con., Cook's Geol. N. J., p. 727. 

 1868. Teredo irregularis Con., Cook's Geol. N. J., p. 727. 



