Small ammonoid assemblages are recorded from the Perapertú  Formation in northern Palencia.  This is a mud-
 stone unit with local platform limestones characterised by carbonate debris flows on the limestone margins.
 T'his unit, of Late Bashkirian to Early Moscovian age, participates in a series of southwards verging thrust slic-
 es North of a major fault zone which originated as the head (leading edge) of a large thrust sheet with an in-
 ternal deformation consisting of thrust slices and at least one nappe structure.  Opposed vergencies at the head
 of this major thrust sheet (Carrionas Thrust Front) and the Ruesga Fault which locally modifies its trace, mark
 the position where the northern branch of the Cantabric-Asturian arcuate fold belt has overridden the southern
 branch in early Westphalian (Langsettian) times.  Two different palaeogeographic areas are found here in juxta-
 position, i.e. the Asturian-Leonese Domain to the South and the Palentian Domain to the North.  The contrast-
 ing stratigraphic developments are summarised in figure 2. Upper Bashkirian and Lower Moscovian formations
 elsewhere in the Cantabric-Asturian orogen are discussed, and the sporadic records of ammonoids in the lower
 part of the Pennsylvanian in various parts of the Cantabrian Mountains are commented on.  The chronostrati-
 graphic significance of the Perapertú Formation is discussed in the context of marine-terrestrial correlations for
 the Late Bashkirian-Early Moscovian time interval. lt is concluded that the evidence from NW Spain suggests
 a position of the base of the Moscovian at the level of basal Westphalian or even within the highest Namurian.
 A brief analysis of the literature shows this position to be different to some of the correlations admitted in re-
 cent publications.
    A newly discovered goniatite fauna from the lower part of the Perapertú Formation contains Brannerocer-
 as sp. indicating Late Bashkirian to earliest Moscovian, and Deleshumardites cantabricus Kullmann gen. et sp.
 nov.  This fauna is figured and described in conjunction with the new subfamily Dombaritinae Kullmann (family
 Delepinoceratidae).  T'he new genus Deleshumardites is erected with "Proshumardites" delepinei Schindewolf,
 1939 as its type species.  Ammonoid descriptions and illustrations include that of Deleshumardites cantabricus
 sp. nov. from strata of an earlier, Serpukhovian age in northern León.