Auloclypeus is very similar to Clypeus, but with aboral petals comparatively weakly developed and less pinching between the anal sulcus and the apical disc. Auloclypeus bridges the morphological gap between Galeropygus, with its non-petaloid ambulacra, and Clypeus, with its extremely well-developed petals. It resembles Nucleolites in petal form, but is differentiated from that taxon by having phyllodes composed of a broad band of pore-pairs arranged in arcs of three. In Nucleolites there is a distinct inner and outer series of pore-pairs.
Mortensen (1948, p. 130) noted that the character of the short posterior oculars is emphasized by Pomel in his diagnosis of his genus Auloclypeus, of which michelini as the first named species must be taken to be the genotype. Mortensen states that he cannot agree with Lambert & Thiery (1921, p. 34) in regarding Auloclypeus as a simple synonym of Clypeus, and that it might be better regarded as a synonym of Echinobrissus (=Nucleolites).
Kier (1962, p. 34) points out that not all species of Clypeus have long posterior oculars (e.g. Clypeus agassizii); furthermore, the test of A. michelini is much larger, broader and lower than in Nucleolites.
P. M. Kier 1962. Revision of the cassiduloid echinoids. Smithsonian Miscellaneous Collections 144 (3) 262 pp.
J. Lambert & P. Thiery 1909-1925. Essai de nomenclature raisonnee des echinides. Libraire Septime Ferriere, Chaumont, 607 pp., 15 pls.
T. Mortensen 1948. A monograph of the Echinoidea: 4 (1): Holectypoida, Cassiduloida. Reitzel, Copenhagen, 363 pp., 14 pls.
Pomel, A. 1883. Classification méthodique et genera des Échinides vivante et fossiles. Thèses présentées a la Faculté des Sciences de Paris pour obtenir le Grade de Docteur ès Sciences Naturelles, 503, 131 pp. Aldolphe Jourdan, Alger.
