Smith.] -"OO [Oct. 2, 



height of the whorl which is 17.5 mm. No measurements of this rela- 

 tion were shown on the Russian specimen. 



This description applies onlj" to the adult shell, the relative measure- 

 ments of the nepionic and neanic shells being very ditferent. The 

 Arkansas specimen showed onlj- the last whorl, but the young stages 

 have been worked out by Karpiusky,* from whose work the following 

 description is translated : "Around the cylindrical embryonic chamber 

 (PI. xxiii, Fig. 8) are coiled very evolute whorls, whose involution 

 increases gradually, but at first only in slight measure (PI. xxiv. Fig. 8)- 

 So, for example, the fourth whorl embraces at the beginning only about 

 one-fourth of the preceding ; thus the height of the evolute portion of 

 this fourth whorl is six or seven times as great as that of its own invo- 

 lute portion. 



With later stages of growth the involution increases so that the 

 whorls become finally completely embracing, and probably conceal a 

 portion of the umbilicus. Because of this mode of growth the umbili- 

 cus appears at first broad, and increasing rapidly, then only gradually, 

 and finally not at all, while the whorl continues to grow in height with 

 great rapid it j'. Thus, at a diameter of the whorl of four or five milli- 

 meters, the umbilicus is about one-half of the total diameter, and at 

 thirty mm. only about one-fifth. The first and second whorls have a 

 broad elliptical cross-section (PI. xxiv. Fig. 8), while that of the succeed- 

 ing whorls becomes higher, with the long elliptical axis vertical (PI. xxiv, 

 Fig. 6), and then finally the fianks are bounded bj' almost parallel lines 

 and the siphonal side is only slightly arched." 



Ontogeny. According to Karpinsky,f the first or typembryonic stage is 

 latisellate, that is the suture consists of a broad abdominal saddle ; this 

 saddle is next divided by a broad siphonal lobe (PL xxiii. Fig. 7 k 



The next stage corresponds to the genus Ibergiceras Karpinsky, of which 

 Oon. tetragonus Roemer, of the Upper Devonian, is the type ; in this 

 the whorls are broad, low and only slightly embracing, the umbilicus 

 wide and shallow. The sutures consist of a long rather narrow sipho- 

 nal lobe, and two bi'oadly rounded lateral lobes. This is the nepionic 

 or larval stage (PI. xxiv, Fig. 9a). In the continuation of this stage the 

 whorls become higher, and the lobes more complicated, corresponding 

 to the genus Frolecanites, of which Gon. henslotci Phillips and Gon. 

 serpentinus Phillips are types. 



In the next stage the shape of shell does change materially, but the 

 siphonal lobe becomes three-pointed (PL xxiv, Fig. 9&); this is the 

 neanic or youthful stage, and corresponds to the genus Puraprolecanites 

 Karpinsky, of which the type is Gon. mixolohus Sandberger (not Phil- 

 lips) (Verstein, Rhein. Schichten-Systein in Nassau, p. 07, PL iii, Fig. 

 13?; PI. ix, Fig. 6). 



The further development consists in the division of the first lateral 



* Ammoiicen der Artinsk-Stvfe, p. 8. 

 t Oji. cit., p. 4 et seq. 



