LAMELLIBRANCHIATA FEOM THE MIDDLE MARL BEDS. 201 



as coming from "Timber Creek, N. J," judging from the lithological char- 

 acters of the specimen. Consequently, I have copied his figures here, and 

 give the species as a New Jersey form for this reason. 



TEREDIDiE. 



Genus TEEEDO Linuseus. 



Teredo tibialis. 



Plate XXVI, Figs. 19-22. 



Teredo tibialis Morton. Synopsis, p. 68, PI. IX, Fig. 2. Gabb, Synopsis, p. 174. Meek, 



Cbeck-]i.st, p. 16. Geol. Surv. N. J., 1868, p. 727. 

 Folorthus tibialis (Morton) Gabb. P. A. N. Sci., 1861, p. 366. Ibid., 1872, p. 259, Plate 



VIII, Figs. 1-7. 



The remains for which this specific name was proposed by Dr. Morton 

 consist of long, flexible shelly tubes, varying in thickness from more than a 

 fourth of an inch at the lower end to often less than a sixteenth of an inch at 

 the aperture. They are usually compactly massed together, and form a layer of 

 from four to six inches in depth and of considerable lateral extent at Timber 

 Creek, New Jersey. When densely packed together they are comparatively 

 straight in their direction, but when more loosely arranged they are often bent 

 and distorted into every conceivable shape. Often at the lower end of the 

 layer the tubes are bent and appear to have had a nearly horizontal direction, 

 as though they had come in contact with some hard substance into which it 

 was difficult for the mollusk to penetrate, and it had consequently taken a 

 dii'ection parallel to its surface. When the tubes are carefully examined they 

 are found to be rounded at the bottom, aud in rare cases appear to have addi- 

 tional septa, as if the animal had for some reason partially withdrawn from 

 the lower end of its length and formed a new bottom to its burrow. I have 

 never seen more than one of these septa in a tube, but have often seen 

 tubes broken at a septum near the middle of its original length. Mr. Gabb 

 figures one, however, in which he represents three of these septa besides 

 the terminal one. The tubes are more or less irregularly constricted 

 throughout their entire length, giving them a somewhat wrinkled appear- 

 ance. At the upper end of the tube there is also a series of partial septa, 



