FOSSILS OF THE HUDSON RIVER GROUP. 99 



conditions under which it presents itself are of such a nature as to make 

 it one of considerable interest. The specimen consists of an inner sep- 

 tate tube of a little more than five inches in length, with a diameter at 

 the lower end of about three-eighths of an inch, by abouj; seven-eighths 

 at the upper end, giving an increase of half an inch in the length of 

 five inches, or of one-tenth of the length. This tube is surrounded by- 

 two others, one within the other; each of the three being separated by a 

 space of about an eighth of an inch on either side, giving to each about 

 the same degree of expansion. The spaces between the tubes are filled 

 with sedimentary matter; that between the inner and middle tube being 

 composed chiefly of finely comminuted organic remains, while that be- 

 tween the twoouter tubes is composed of fine silt chiefly, and in some places 

 with crjrstalline matter. The septa of the inner tube are closely arranged, 

 eight of the spaces measuring one inch where the upper end of the space 

 measured is seven-eights of an inch in diameter, those below being a lit- 

 tle closer. These are all either empty spaces, or filled only by crystal- 

 line matter. There is not the least evidence of septa or partitions of 

 any kind across the spaces between the several tubes. The specimen 

 lies imbedded in the rock, and weathered away to near the center of its 

 diameter, but the section at the end shows that the inner tubes rest upon, 

 or nearly upon, the inner surfaces of the surrounding ones, as though 

 they had settled to this position after they had been imbedded in the 

 sediment. These conditions would seem to indicate that there had been 

 no very intimate connection between the several tubes, and that the 

 spaces between the outer ones and the inner septate portion had been 

 open to the access of foreign matter, while the inner septate portion had 

 been closed, or that the outer tubes had been independent of each other, 

 and of the inner ones, and had only drifted into each other by accident. 

 If this has really been the case, these outer tubes must be only the term- 

 inal chambers, or chambers of habitation, and must have been of unusual 

 length, as the degree of tapering would carry the middle tube to within a 

 few inches, if perfect at the lower end, of the point of a specimen nearly 

 or quite fifteen inches in length? The probability, however, is that they 

 are only fragments of outer chambers that have drifted upon the inner 

 ones by accident. 



At first sight the specimen might be taken for a beautifnl example of 

 the genus Endoceras; but true examples of this genus are septate in the 

 outer tubes, while the inner ones are free from septa. The reverse is, 

 however, the case in the example before us. 



Formation and locality : The speciraen occurs in a fragment of limestone composed 

 principally of comminuted organic remains, and from its character appears to have 



