descbiptio:n of species. 11 



they approach each other closely. There is an outward slope also on the 

 back of the ribs, away from these lines. At the summit of the ribs the 

 angular depression measured from line to line is much broader than at their 

 base. The grooves seen on the stem below the sheaths are caused by the 

 gradual approach to each other of the raised lines, and when they meet the 

 grooves terminate. The imprints of these grooves, seen in relief, appear as 

 gradually tapering, sharply-defined, keeled ridges. Plate II, Fig. la, which 

 represents a portion of the sheath magnified, shows these features. It will 

 thus be seen that these lines determine the entire character of the ribs and 

 teeth. They can very rarely be seen showing all the details that I have 

 given here. I was fortunate enough to obtain at Clover Hill, in a fine- 

 grained dark shale, specimens of the surface of the stem, and of its impres- 

 sions on the shale, showing the smallest details with the nicety of a litho- 

 graphic imprint. Plate II, Fig. 2, represents a portion of the stem in which 

 the internodes are short, and on which the diaphragms do not appear. Plate 

 II, Fig. 1, represents the largest specimen that I have seen on which the 

 sheaths are displayed. On it the diaphragms show themselves. I have 

 given 80 as the greatest number of teeth, as this is the largest number 

 indicated on any impression seen by me. As the specimens represent stems 

 which are pressed perfectly flat, I conclude that the number of ribs and 

 teeth are at least twice as many as those seen on the surface exposed to 

 view. Judging from the diameter of the casts of the interior of the stems, 

 which sometimes occur perfectly cylindrical in shape, the thickness of the 

 largest stems is about 8 to 9 centimeters. An average stem has a diameter 

 of about 6 centimeters. On a stem of about this diameter, found at the 

 Aspinwall Shaft near Manakin, four internodes exist, which give the follow- 

 ing measurements: Lowest internode, 45 millimeters; second internode, 51 

 millimeters; third internode, 57 millimeters; fourth internode, 59 millime- 

 ters. This portion of the stem was evidently some distance from the base. 

 It will be seen that the increase in length is quite gradual. The lower 

 internodes are often so short that the furrows below the sheaths overlap the 

 sheath of the internode below. 



Plate I, Fig. 2, represents what is probably the rhizome of an Equise- 

 tum, and probably of E. Bogersi. The specimen is a fragment of a flat- 



