NO. 1690. ON EDESTU8 AND RELATED GENERA— HAY. 55 



the blade forms, in Lissoprion, about one-half the total height of the 

 tooth. 



The apical angle of the teeth before us is obtained by drawing lines 

 from the apex to the opposite ends of the cutting edges. This angle 

 varies with the size of the teeth. In the teeth originally described, 

 the largest yet found, the apical angle is 48°. In the largest teeth of 

 pi. 14, fig. 1, the angle is 35°, while in the teeth of the specimen 

 represented by pi. 14, fig. 2, it is 32°. The smallest teeth appear to 

 have the same angle as just given. It is seen, therefore, that the angle 

 increases rapidly in the largest teeth. Karpinsky has stated ** that in 

 IIelicop7'ion hessonowi the apical angle is 30°. The present writer 

 makes it 45°. 



The cutting edges of the teeth of LissopHon were originally 

 described as being smooth ; but some of the newer specimens show 

 that these edges were sometimes feebly crenulated. 



The middle portion of each tooth is short, convex posteriorly, con- 

 cave anteriorly. It passes insensibly into the third portion. The 

 latter is naiTowed to a point below and turned toward the older parts 

 of the coil. In the smaller and medium-sized teeth its extremity 

 reaches forward to a point opposite the hinder border of the second 

 tooth in advance. In the larger teeth it extends forward only to the 

 middle of the tooth immediately in front. Each tooth touches its 

 l^redecessor and its successor only at the base of the blade. The 

 median and third portions of the successive teeth are separated by a 

 space very narrow and varying little in relative width throughout the 

 series. In IleVicopr'ion hessonoiri the interdental spaces vary con- 

 siderably, being much wider relatively between the smaller teeth.'' 

 All the teeth of Lissoprion were covered with enamel, but this has, 

 in the specimens at hand, been altered or removed. It seems to have 

 been traversed by narrow ridges, which radiated from the apex of the 

 tooth. 



Fig. 2, of pi. 14, furnishes a good illustration of the shaft and its 

 relation to the teeth. It will be observed that a wide band of the 

 shaft is exposed below the enameled processes of the teeth, the width 

 in the case of the specimen figured being G mm., one-fifth the height 

 of the teeth and the shaft taken together. In Helicoprion there is far 

 less of the shaft visible below the teeth; according to Karpinsky's 

 figures, about one-fifteenth of the height of the teeth and the shaft. 

 Text fig. 7 shows a section through the axis of the second tooth from 

 the right. It is seen that the sides of the shaft are convex and that in 

 the lower border there is a rounded notch. This represents a gutter 

 that runs along the inner border of the shaft. A similar gutter occu- 



" Verhandl. russ.-kais. miu. Gesellsch. St. Petersb., 2d ser., vol. 26, 1898, 

 pp. 383. 402, fig. 23. 

 ^Idem, p. 394. figs. 24-29. 



