IV.—Notes on Ammonites

Extract

As an illustration of the difficulties encountered in basing the classification on some peculiarity of the Ammonoid suture-line the case of the two families Macroscaphitinæ and Crioceratinæ may again be referred to, the former of lytoceratid, the latter of hoplitid origin. Distinction between these two families was based on the bifid or trifid characters of the first lateral lobe. Hamulina nitida, v. Koenen, which shows very nearly equal-sized suture elements, has the trifid first lateral lobe of the type-species of Hamulina, namely S. dissimilis, d'Orbigny, but the plain shell of the lytoceratid Anahamulina. Hyatt put the latter into his family Macroscaphitidæ, but the former, and also the clearly lytoceratid Pictetia, into Ancyloceratidæ, i.e. even into a different sub-order. But Anahamulina subcylindrica, d'Orbigny, sp., i.e. the type-species itself, has a nearly trifid first lateral lobe, though it is connected through A. Lorioli, Uhlig, sp. (with a sub-bifid first lateral lobe), with typically lytoceratid forms. In ornament and coiling also Hamulina resembles certain lytoceratid forms (compare e.g. the various forms of Macroscaphitinæ figured by Uhlig).