Subdichotomoceras Hourcqi (Collignon, 1960): A very interesting ammonite sold to us as a "
Perisphinctes" by a dealer from Madagascar. While checking the lot this one turned up with two constrictions followed by a single simple rib.
Perisphinctes are not expected to have constrictions but
Subdichotomoceras is. Referral to Collignon's "Atlas Des Fossiles Caracteristiques De Madagascar, fascicule VI (Tithonique), 1960" quickly turned up a description that exactly matches this specimen. Refer to specimen number 592 in the above mentioned work.
This is an excellent Subdichotomoceras specimen about 3.4 inches (87 mm.) across weighing in at 7 ounces. The specimen is described in Madagascar as "nacreous", most of the perisphinctids we see from Madagascar are "in the white" with the original shell completely gone. This "nacreous" specimen has much of an apparently original shell remaining. This is one of three ammonite specimens we got this year from the Upper Jurassic deposits at Sarodrano in SW Madagascar.
Click the image for more views of the specimen.
Stock No.:
08.485
