Hyatt.] H 228 [December 2, 



that species in the smaller size and greater proportional bulk of the 

 whorls, the breadth and depressed convex form of the abdomen, and 

 the raised siphonal line. Several specimens of this species in the 

 collection at Stuttgart from Balingen showed living chambers, as 

 pointed out to me by Prof. Fraas, always shorter than in P. plan- 

 orbe, and the septa distinct. The peculiar folds appearing in some 

 shells, and the form and aspect of the whorls like those of the young 

 Scipionianus, show that their affinities lie in the same direction as 

 those of Scipionianus. Occurs in the Geometricus bed. The originals 

 of Prof. Quenstedt's descriptions from Pforen fully sustained the 

 above, and a fine suite of these at Semur exhibits several forms pass- 

 ing into the young forms of Scipionianus. 



Agassiceras Scipionianum Hyatt. 



Amm. Scipionianus D'Orb., Terr. Jurass., p. 207, pi. 51, f. 7-8. 



This species varies exceedingly ; some of the young occasionally 

 show a crenulated keel ; they may also be either smooth or pilated 

 on the sides, with all the intermediate differences. The abdomens 

 are keeled and occasionally though very slightly channeled. The 

 form of the whorl from the young up may be either very gibbous or 

 comparatively flat. In the young forms the pilae vary from those 

 comparatively thin and depressed to prominent well-defined ones, 

 with or without tubercles; they may also be either very numerous or 

 few in number, and be very distinct or mere thick awkward looking 

 folds. It has been commonly supposed that the affinities of this 

 fossil were with the Margaritatus group but nothing could well be 

 more erroneous. Its development is altogether peculiar and differ- 

 ent and its septa are very distinctly Arietian. 



When old age begins the tubercles are suppressed, the sides become 

 flatter, the geniculse bend less abruptly and curve slightly forward, 

 the pilse reaching to the edge of the channels, these last being in- 

 dicated by shallow longitudinal furrows raised above the level of the 

 abdomen ; the keel still remaining very prominent and sharp. The 

 envelopment even at this age does not exceed one third of the breadth 

 of the whorl. This old age period just before the pilse become obso- 

 lete is very similar to the adult of Asteroceras Collenotii. 



The young of this species has the rotund gibbous volutions so char- 

 acteristic of lozvigatus and striaries. The sides are at first divergent, 

 but they become nearly parallel on the latter part of the second whorl ; 

 the dorsal side also broadens and the umbilical shoulders become 

 more abrupt. On the third volution the sides are entirely parallel, 



