650 CRETACEOUS PALEONTOLOGY. 



1864. Gastrochcsna americana Meek, Check List Inv. Foss. N. 



A., Cret. and Jur., p. 15. 

 1864. Polarthus americanus Meek, Check List Inv. Foss N. A., 



Cret. and Jur., p. 16. 

 1872. Polorthus Americanus Gabb, Proc. Acad. Nat. Sci. Phil. 



(i872),p. 259, pi. 8, fig. 8. 

 1886. Gasstrochcsna Americana Whitf., Pal. N. J., vol. i 



(Monog. U. S. G. S., vol. 9), p. 203, pi. figs. 17-18. 

 1905. Gastrochcefia americana Johns., Proc. Acad. Nat. Sci. 



Phil. (i9os),p. 18. 



Description. — Tubes solitary, elongate-conical, the larger ex- 

 tremity rounded; attaining a length in the largest examples of 

 75 mm., and a maximum diameter of about 12 mm.; the minor 

 diameter is usually about 5 or 6 mm. ; diameter increasing gradu- 

 ally and more or less irregularly, usually being i mm, in a length 

 of fro'm 6 mm. to 16 mm. Surface irregularly marked by annular 

 wrinkles and constrictions arising from what have been the 

 rounded! extremity of the tube at different stages of its growth. 

 Some specimens have almost the appearance of worn specimens 

 of Orthoceras, but with the septa convex towards the larger 

 instead of the smaller extremity. No^ remains of a bivalve shell 

 have ever been observed. 



Remarks. — ^This species, with Morton's Teredo tibialis were 

 placed by Gabb in his genus Polorthus. The two species agree in 

 being the tubes of some form of boring mollusk of which no 

 bivalve shell is known, and apparently in having the tube septate. 

 In the details of their structure the two forms are very different, 

 and it can be hardly possible that they are really cogeneric. Inas- 

 much, however, as it is not possible to determine the exact. generic 

 relations of these tubes at the present time, it seems best to con- 

 tinue them under the name Gastrocliaiena, the genus to- which they 

 were first ascribed and to which they have been most commonly 

 referred. 



Formation and locality. — Vincentown limesand. New Egypt 

 (143), Timber Creek (Gabb). 



Geographic distribution. — New Jersey. 



