660 CRETACEOUS PALEONTOLOGY. 



1864. Teredo tibialis Meek, Check List Inv. Foss. N. A., Cret. 



and Jur., p. 16. 



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

 1872. Polorthus tibialis Gabb, Proc. Acad. Nat. Sci. PhiL 



(1872), p. 259, pi. 8, figs. 1-7. 

 1886. Teredo tibialis Whitf., Pal. N. J., vol. i (Mbnog. U. S. 



G. S., vol. 9), p. 201, pi. 26, figs. 19-22. 

 1905. Teredo tibialis Johns., Proc. Acad. Nat. Sci. Phil. (1905),, 



p. 18. 



Description. Tubes usually compactly massed together in 

 layers which are sometimes as much as 6 inches in depth and of 

 considerable lateral extent, apparently penetrating sand alone. 

 Tubes calcareous, gradually increasing in size from a diameter 

 of less than i mm., to a maximum diameter of about 6 mm. ; 

 usually more or less irregularly constricted at intervals ; straight 

 or more or less wavy throughout the greater part of their length, 

 sometimes throughout, but often becoming bent and contorted 

 towards their larger extremity, which is always rounded. In the 

 smaller extremity of the tube, in the terminal 5 or 6 mm., is a 

 series of six to eight transverse septa, convex towards the smaller 

 extremity of the tube, perforated centrally by an elliptical slit of 

 greater or less size; the smaller extremity of the tube often 

 constricted longitudinally so as to form a double opening; just 

 below the terminal series of septa the casts exhibit a continuous 

 annular muscular scar with two long inverted U-shaped pro- 

 longations towards the aperture on opposite sides, and similar 

 U-shaped backward extensions between. Towards the larger ex- 

 tremity of the tubes there are from one to three, more or less 

 remote, transverse septa, convex towards the larger extremity 

 of the tube. 



Remarks. This species sometimes forms large masses in the 

 Vincentown limesand, and differs from the Teredo-like tubes 

 found in the lower formations of the Cretaceous beds of New 

 Jersey in apparently having the habit of boring into the sand of 

 the sea bottom instead of into masses of wood. The tubes also- 

 differ from those of the lower beds in the presence of transverse 

 septa of two sorts, and in the entire absence of any bivalve shelL 



