54 PROCEEDINGS OF THE XATtOXAL MU8EUM. vol.37. 



The small teeth of fig. 1, pi. l-t, present only a part of their upper 

 portion, or blade. 



The specimen represented by fig. 2, pi. 14, presents wholes or 

 parts of 13 teeth and the corresponding part of the shaft. Plate 15 

 is taken from the specimen that displays the whole of the spiral. 

 Unfortunately the matrix is of such a dark color that the fossil does 

 not show as distinctly as is desirable. However, from this it is 

 learned that the structure, dentition or spine, whichever it may be, 

 consisted of a shaft of a little more than two and a half coils and a 

 series of enameled teeth occupying the outer border of the shaft. The 

 inner coil with its minute teeth was, of course, first produced. It 

 is not probable that the smallest teeth seen are the first that the animal 

 possessed. Some smaller teeth and their shaft may be hidden in the 

 obdurate matrix, but it is more probable that they had been lost by 

 the animal long before its death. 



The greatest diameter of the specimen, measuring from the apex 

 of the last tooth to the apex of the one on the opposite side of the 

 coil is IGO mm. The inner coils were not in contact with the outer 

 coil nor with each other. The apices of the teeth at the beginning of 

 the second coil are removed by about 10 mm. from the inner border 

 of the shaft ; the innermost teeth approach within 3 mm. of the shaft. 

 It is impossible to determine exactly the whole number of teeth. An 

 estimate made as accurately as possible indicates that there were 32 

 teeth in the outer coil, the same number in the preceding coil, and 22 

 teeth in the portion remaining of the innermost coil, in all 86 teeth, 

 as against 130 in Ilelicoprion hessoyiowi; but the latter species pos- 

 sessed about one more coil than did the species here described. In 

 Karpinsky's species there were 36 teeth in the innermost coil, 43 in 

 the next, and 51 in the outer. 



Karpinsky showed that the teeth of his species might be regarded 

 as consisting of three portions. The first includes the cutting blade, 

 extending from the apex to the points where the edges of the blade 

 come into contact with the blades of the succeeding and the preceding 

 teeth, respectively; the third portion includes that part that is nar- 

 rowed and turned toward the older teeth of the series; the second 

 portion is found between these two. In the larger teeth of Helicop- 

 rion the intermediate portion occupies half or more of the height of 

 the tooth; in the case of the smaller teeth it becomes reduced in 

 importance and may become merged into the third portion. In 

 Lissoprioii this middle part may be said to be present in all the 

 teeth, but to be relatively unimportant. In Helieoprion the blade is 

 relatively longest in the oldest, or smallest, teeth, forming some- 

 times more than half the height of the tooth, while in the largest 

 teeth it forms onlv about a fourth of the height. In all cases 



