Description. Type Prolyelliceras peruvianum Spath, 1930. Moderately compressed and high-whorled, with straight to flexuous, radial or proverse ribs. The ribs cross venter, flattening in juveniles of some species. They bear 2 to 4 tubercles per flank, with at least siphonal and ventrolateral clavi. Primitive morphologies lack lateral tubercles. Evolute species have punctiform or claviform lateral tubercles during mid-growth, which may disappear on body chamber. The most evolute forms sometimes have umbilical tubercles, but not in adult stage (Latil et al., 2009). From Lower Albian (tardefurcata zone) to the beginning of Middle Albian (benettianus zone). South-Eastern France, Austria, Algeria, Tunisia, Venezuela, Colombia, Peru.
Species. Latil et al. (2009) revised the Tethyan species P. gevreyi (Jacob, 1907), with two tubercles per flank (siphonal and ventrolateral). P. flandrini (Dubourdieu, 1953) is a thick variant according to Latil (2011). Robert (2002) describes a Peruvian group with higher whorls. Its forms with two rows of tubercles (per flank) include P. peruvianum, with thin, widely spaced ribs, and P. lobatum (Riedel, 1938), with broad, more closely spaced ribs. Three-row forms include P. prorsocurvatum (Gerhardt, 1897) with flexuous ribs and lateral tubercles disappearing with age, P. ulrichi (Knechtel, 1947), with rows present from the outset, P. mathewsi (Knechtel, 1947), with lateral tubercles appearing around 5-6 cm, and P. cotteri (Spath, 1930), with numerous ribs and tubercles only slightly elongated . We will see that Robert's P. cotteri does not correspond to Spath's species. The Colombian species P. apuloense Etayo-Serna, 1979, has umbilical bullae, therefore 4 rows, but they are absent in the adult. Gerhardt's figure on the right shows a P. prorsocurvatum: the punctiform lateral tubercles disappear at the bottom of the last whorl.
Remarks. This genus and Lyelliceras are homeomorphs: they evolved into an identical form but do not share a common ancestor. Lyelliceras has four rows of tubercles at all ages: one siphonal, one ventrolateral, one lateral, and one umbilical. It derives from Tegoceras and occupies the steinmanni and benettianus zones. In Prolyelliceras, the umbilicals are absent or ephemeral, and some species lack lateral tubercles. The suture resembles that of Lyelliceras, but with fewer elements and wider saddles. The genus coexists with Lyelliceras in Peru and Colombia, but it appears as early as the basal Albian (tardefurcata zone). Its ancestor is unknown. In Wright's Treatise (1996), Prolyelliceras is placed in the Lyelliceratidae, alongside Lyelliceras. We follow Latil et al. (2009), who move it to a new family within the Acanthocerataceae, the Prolyelliceratidae. Etayo-Serna (1979) created a convenient genus, Ralphimlayites, for Prolyelliceras with lateral tubercles like P. ulrichi. He is followed by Robert (2002), but Wright (1996), Kennedy & Klinger (2008) and Latil et al. (2009) consider it a synonym of Prolyelliceras, arguing that these tubercles can appear late and/or disappear with age.