Megalograptus Welchi. 345 



spines to the next saw-tooth, and so on, to the top ; thus dividing the 

 frond into six sections. The first section is quite irregular, because of 

 broken edges. The second section has four spines, one of which has 

 its point directed downward, another has its point directed upward, 

 and the other two are directed nearly at right angles to the frond. 

 The projection, like a saw-tooth, on the opposite side, may have been 

 produced by pressing together the body, which, at this place, was 

 suddenly contracted. Indeed, the saw-tooth projections all seem to 

 me to have been formed in this manner, and, therefore, to represent 

 the amount of the contraction of the frond at each tooth. The si^ines, 

 too, may not have been one above another, because compression would 

 give them that appearance, whether they were in line or not, and one 

 specimen examined indicates that they were not placed in line, one 

 above the other, as they appear. The third section has evidently had 

 one spine broken off from the lower side, and, therefore, had three 

 spines, only two of which remain. The fourth section has the appear- 

 ance of having had three spines, but the lower two represent a broken 

 spine which was longer than the upper one. The fifth section has two 

 spines, the upper one of which is the longest. The sixth section ter- 

 minates in a spine at the top, and appears to have borne a spine upon 

 the opposite side from the other spine. Part of the film has been 

 decorticated from this specimen, and hence the exact surface covered 

 by the cells could not be ascertained. It is quite clear, however, that 

 the cells were not placed on or close to the spines, while they covered 

 the greater part of the balance of the frond. The line separating the 

 celluliferous part from the non-celluliferous part in the engraving is, 

 therefore, only approximately correct. 



Figure 37 may be separated into three sections : the lower one, having 

 three spines, and being broken at the lower end, showing the film on 

 the opposite side, and being compressed to one eighteenth of an inch in 

 thickness ; the second section has two spines ; the third section may 

 be somewhat fragmentary on the top. The part of this specimen 

 showing the cells is quite clear, but some of the film is removed from 

 the central part and toward the spines, consequently the cells may 

 have extended nearer to the spines than they are shown in the figure. 



Another specimen, at a point where it is one inch in diameter, bears 

 five spines, two of which project downward, and two upward, the 

 upward projecting spines being the longest. It is broken off an inch 

 and a half below these spines, where it rapidly enlarges to one and a 

 half inches in diameter. 



The specimens were all found in a bed of blue marl, in the upper 

 part of the Cincinnati Group, near Clarksville, Clinton county, Ohio, 



