The Genus Helicoceras

The members of the genus Helicoceras were formerly placed in the genus Gyroceras.A study of the literature, however, shows that this latter name cannot be applied to the species other than Gyroceras ammonis, and for reasons to be shown shortly that name is not valid because of synonymy.The genus Gyroceras, based on G. ammonis, was erected by Corda^ in 1837.His description of the original species runs as follows: ''Acervulis atris, confluentibus, stromatis strato inferiore atro; superiore luteo, hyalino, celluloso; floccis infra atris, supra attenuatis luteis; sporis ovahbus discoideis, depressis."It readily can be seen that the presence of a two-layered stroma sharply sets off Corda's species from the non-stromatic ones that make up the remainder of the genus.These latter are parasitic or weakly so, and their vegetative hyphae, although branching, never aggregate to form a stroma under the sporogenous area.A careful examination of the original figure illustrating G. ammonis makes it obvious that the present-day conception of the genus is founded on misinterpretation.The "strato superiore" is definitely a layer of short conidiophores beyond which the curved sterile hyphae project.According to Corda, these sterile hyphae break into ovoid discoid spores, a statement that seems partly to have been the cause of the misconception of his genus, and one that needs confirmation before final acceptance.Even though this doubtful point were settled, Corda's genus is not that of later investigators and, in fact, should be relegated to synonymy, as is done in the