Perisphinctid ammonites from the late Jurassic formations near Tulear, Madagascar.
Examination of the "Perisphinctes" ammonites from Madagascar we have for sale reveals a problem.  The ammonites, sold to us as "Perisphinctes" have several different body shapes.
Identification cannot be positively made as the Malagasay who recover these fossils don't record the sedimentary horizon information vital to positive identification.  We have constructed a computer database on these "perisphinctid" fossils and have been able to use it to suggest identifications.  In most cases, one or two fossil types are suggested and resort to Collignon's pictures can get closer to a diagnosis but some are similar enough that differentiation is not possible. 

The specimens we currently have for sale are all genus Aulacosphinctoides  of various undetermined species. 
A. infundulum, A. ambilobensis, A. guthieri are all possibilities.

Ref. Collignon, M.; ATLAS DES FOSSILES CARACTERISTIQUES DE MADAGASCAR, Fascicule VI, (TITHONIQUE) Service Geologique, Tananarive 1960.