DESCBIPTION OF SPECIES. 15 



The casts called Calamites arenaceus are marked by closely placed fine 

 lines. Brongniart has given a good figure of one of them, which was sent 

 to him from the Richmond Coal Field. It appears in the "Hist, des Veg. 

 foss.," plate xvi, fig. 1, with the name Calamites Suckowii, var. 6. The plant 

 now in question seems to have been far larger than Equisetum Eogersi. 



I have found in the collections of the University of Virginia several 

 specimens of this plant from an horizon not indicated. One of them is 

 the sandstone cast of the interior of this plant, over 12 centimeters thick. 

 Another cast is 17£ centimeters thick. The specimen figured is a small 

 portion of a flattened cast in fine-grained shale, which is 15 centimeters 

 wide, and shows an internode 17 centimeters long. The rounded ribs, the 

 articulations of the leaves indicated by Professor Rogers, and the great 

 size of the stem appear to indicate that this plant is a Schizoneura, but 

 until the impression of the exterior of the stem is seen its true character 

 cannot be positively determined. 



Bunbury, in the third volume of the "Quarterly Journal of the 

 Geological Society," under the head of Calamites arenaceus, says that some 

 of the impressions called by that name are as much as 20 centimeters in 

 diameter. He does not say whether this measurement is the width of a 

 flattened stem, or the thickness of a cylindrical one. It is to be presumed 

 that the latter is meant. These dimensions belong, not to Equisetum 

 Bogersi, but to the supposed Schizoneura now in question, and it is prob- 

 able that Bunbury had casts of this plant, on which the characteristic 

 markings were not well shown. This occurs usually in the case of sand- 

 stone casts. 



The cast depicted in fig. 1 , on the parts where the coaly matter of the 

 imprint is preserved, shows the characters above given quite distinctly. 

 The original exterior of the casts, however, is very rarely preserved, for 

 the prominent semi-cylindrical ribs are easily rubbed off, and leave in their 

 place impressions looking like flat ribs. This feature is shown at a in the 

 lower part of fig. 1. The ribs run across the nodes, usually suffering a 

 slight deflection in their course, but sometimes they are interrupted, and 

 abut against the interval between the ribs above. This, however, is rare. 

 The space between two adjacent ribs appears to be rather rounded than 



