90 



Report of the State Geologist. 



of the shell toward its adult condition the auxiliary lobes have been introduced 

 before the sharpening of the main lobes and thus the Lutheri stage of the 

 lobe has been hastened over and obscured. Nevertheless, there is clearly a 

 place for it among the stages of Gon. iynx and the stage at which the Lutheri 

 condition was skipped, could doubtless be made out with the study of somewhat 

 more complete material. Of Gon. Lutheri we have a very complete knowledge 

 of the developmental phases in all of its features and shall show that the ephebic 

 suture is an outcome of a manticoceran condition preceded by a simpler 

 anarcestian stage There is probably no good reason for not incorporating 

 iron, inyx in the genus Beloceras, notwithstanding the fact that its condition 

 with reference to JBel. multilobatum is immature ; but the subdivision of the 

 principal lobes and saddles in the former species is well established and the 

 difference in the two is that of the extremes to which this division has been 

 carried. An instructive instance of another intermediate condition more pro- 

 gressed than that of Gon. iynx is the Gon. Kayseri, Holzapfel, from the middle 

 Devonian of Martenberg,* which bears in its mature stage eight mostly acute 

 lobes and saddles, and in its degree of umbilication is a nearer approach to Gon. 

 iynx than to Gnu. multilobaium. For Gon. LutJieriwe have proposed to intro- 

 duce the generic term Probeloceras, on account of the unimpaired simplicity of 

 the mature suture. 



(Family Prolecanitidae, Hyatt.) 

 Probeloceras, gen. nov. 

 Discoidal, laterally compressed, umbilicated shells, with a narrow peri- 

 pheral band, concave and with raised edges in immature stages, convex in the 

 adult. Suture with a single large and acutely angled lateral saddle, and two 

 acute lobes; ventral and sublateral lobes rounded. Early stages show a 

 gradual derivation of the suture from a manticoceran outline by the sharpen- 

 ing of the principal saddle and sublateral lobe. 

 Type, Goniatites Lutheri, Clarke, 1885. 



Probeloceras Lutheri, Clarke, 1885. f 



Plate VII, Figs. 1-10. 



General Form. Ad nit. 

 The full-grown shell is very widely umbilicated, disk-shaped, with 

 narrow, deep whorls, subsagittate in section in all later growth-stages. The 

 sectional outline gives the greatest convexity toward the umbilicus, and on 

 the umbilical margin the slope is quite abrupt. The venter bears a sharply 

 denned median surface extending like a tire about the periphery of theiexposed 



*See Palaeontoicraphica, viif , C, p. 14, lxv, figs. 7-10. 



tSee unci of description for a full bibliography of the sptcits. 



