Hyatt.] 22 [May 20, 



-33goceras Leigneletii Hyatt. 



Amm. Leigneletii D'Orb., Terr. Jurass., Ceph., p. 298, pi. 92. 



Amm. angulatus compressus Quen., Die Cepli., p. 75. 



The same class off acts divides this species from Charmassei that we 

 used to show the differences between the latter and angulatus 

 — namely that the young differ as well as the old in some specimens. 



The differences are very great between the fifth whorl (about) of 

 Leigneletii, and the same age in Charmassei. The tubercles are more 

 prominent on the edge of the abdomen, the pilse more depressed on 

 the sides, and their terminations tubercular on the edge of the abdo- 

 men, which instead of being a broad, rounded space, is a flattened 

 zone. The reduction of the abdomen of course occurs in all species 

 of this group, but in other species, except Boucaultianus, it is found 

 only during the senile stage. 



A specimen of Boucault's Collection, labelled Amm. Charmassei, is 

 probably the young of this species. If so, the young shell differs 

 from Charmassei in having laterally compressed whorls, like those of 

 its own adult, much finer pilse, not so prominent and near the abdo- 

 men, bifurcating very regularly. The smooth lateral zones found on 

 the fifth volution are not indicated on the fourth wliorl in this speci- 

 men, and it resembles at this time in the form of the whorl, the pilse 

 and the abdominal channel, a much older stage of growth which 

 occurs in Charmassei. 



Amm. angulatus compressus of Quenstedt may also in part belong 

 to Charmassei, but the two specimens from Museum Stuttgart are 

 apparently of this species only. The development in one of these 

 specimens covers about two-thirds of the sides of the eighth whorl, 

 and about the same age the pilse again cross the narrow abdomen, 

 obliterating the siphonal depression or bare tract, and introducing a 

 series of crenulations instead. This is a return to the young condi- 

 tion, and indicates the first degradational or old age period. Of 

 course it is not intended by this to deny that there are no young which 

 closely approximate to the young of Charmassei. On the contrary 

 some specimens are apparently identical in all respects, except the 

 greater flatness and the earlier period at which the involution ap- 

 pears to be shown. In "fact the species are connected by numerous 

 transitional forms with Charmassei. 



