Middle Cambrian fossils from Tizi n'Tichka, the High Atlas, Morocco .1. Introduction and trilobites

New finds of the trilobites Cobboldites tichkaensis Geyer, 1988, Pseudocobboldia pulchra (Hupe, 1953), Protolenus (Protolenus) densigranulatus Geyer, 1990, Latoucheia (Latoucheia) tichkaensis Hupe, 1953, and Acanthomicmacca neltneri Hupe, 1953, from the basal Middle Cambrian near the peak of Tizi n'Tichka in the central High Atlas, Morocco, supplement the known morphology of these species; the trilobites Acanthomicmacca new species, Oreisator tichkaensis new genus and species, and ''Parasolenopleura'' sp. from that locality are new. Acanthomicmacca neltneri is the first-species of the genus and family that is described and figured in detail in terms of morphologic plasticity and ontogeny; Oreisator tichkaensis is the first ptychopariacean trilobite formally described and based on material from Africa. Trilobites and other fossils from the locality suggest a strong affinity to other Mediterranean and to Avalonian faunas, which is well supported by helcionelloid and hyolith genera.