PERISPHINCTES. 



curvature, it agrees entirely with the former, that we must re- 

 gard this sculptureless rod, strange as it may seem, as one of the 

 Ornata much elongated ; in regard to this agreement with the 

 initial whorls of Ancyloceras, Quenstedt had already noticed it. 

 From Baculites, Baculina is distinguished by one-pointed lateral 

 lobes. In order to avoid making a new name. Baculina may be 

 here applied. 

 BACULINA ARCUARTA, Quenst. T. 100, fig. 517. 



Genus PEEISPHINCTES, Waagen. 



Shell mostly with wide umbilicus, with rounded external side, 

 sculpture consisting mostly of straight, undivided, not nodose 

 ribs ; margin of aperture simple or with ears, with a constric- 

 tion ; also isolated constrictions on the inner whorls. Length of 

 body-chamber two-thirds to one whorl, mostly scarcely embra- 

 cing one circumference or turn. Lobular line similar to Stephano- 

 ceras, usually somewhat more deeply notched, with a dependent 

 sutural lobe. Aptychus divided, calcareous, very thin, exter- 

 nally granular. 



The genus Perisphinctes embraces the old group of the Planu- 

 lata, with the exclusion of 'the Liassic forms, which belong to 

 Stephanoceras ; the geologically oldest species of typical Peri- 

 sphinctes is P. Martinsi, from the upper part of the Lower 

 Oolite ; the genus branches off in all probability from Stephano- 

 ceras, but the relationship between the two is however not yet 

 fully known. The maximum development is reached in the 

 upper Jurassic ; in the Cretaceous there are yet few representa- 

 tives which have retained their character in purity, and instead 

 numerous diverging series branch off', which must be separated 

 as distinct genera, and which embrace the majority of the creta- 

 ceous Ammonites. 



We here place also another group provisionally, which perhaps 

 deserves to be elevated into a distinct genus. To Perisphinctes 

 fraudator, Zitt., from Stramberg, which still presents the type 

 of the genus some Stramberg forms are allied with a deepened, 

 smooth external furrow and stronger sculpture on the body- 

 chamber, as Per. microcanthus, Opp., Kollikeri, Opp., symbolus, 

 Opp. To these certain forms from the lower Neocomian are 



