The Echinoid Directory

Contributed by Andrew Smith, January 2017

Pseudomilnia Smith, 2016, p. 103

Diagnostic Features	Apical disc opening large; plating not preserved in any specimen; distinctly elongated with width 70% of length. Ambulacral plating trigeminate, plate compounding acrosaleniid at ambitus and adapically, Pore-pairs uniserially arranged at the ambitus and above but expended forming prominent phyllodes over most of the oral surface. Single primary tubercle on compound ambulacral plates at the ambitus and adorally, but adapically these tubercles become very small and there is a wide perradial band of uniform granulation. Interambulacral plates with a single large primary tubercle flanked by zones of fine uniform granulation. On ambital and adoral plates these primary tubercles are contiguous but adapically they rapidly diminish in size and move close to the adradial border. All primary tubercles are perforate and strongly crenulate. Adapical regions of the test covered in a dense uniform granulation. Peristome large, flush, with strongly rimmed buccal notches associated with naked adradial zones. Spines, pedicellariae and lantern unknown.
Distribution	Middle Jurassic (Aalenian) of England and France.
Type	Acrosalenia miliaria Paris, 1908, by original designation.
Species Included	No other species included
Classification and/or Status	Euechinoidea; Calycina; Salenioida; stem group (acrosaleniid)
Remarks	Pseudomilnia resembles Milnia in possessing greatly reduced adapical interambulacral tubercles and in having tiny adradially positioned ambulacral tubercles above the ambitus. In both, the apical disc is strongly elongate, but the apical disc plates in Pseudomilnia were apparently less firmly attached to the corona, as in none of the known specimens is apical disc plating retained. Plates at and above the ambitus are covered in a dense, uniform, fine granulation, forming a wide perradial zone in the ambulacra and broad adradial and interradial bands in the interambulacra. However, whereas Milnia has a sunken peristome with pore-zones remaining uniserial right to the edge of the peristome, Pseudomilnia possesses broad adoral phyllodes that start in the subambital region and incorporate a large number of pore-pairs. This immediately distinguishes the two genera and implies a very different life-style for the two. Recrosalenia is a poorly known taxon from the Bathonian-Callovian of Somalia and differs in having uniserial pore-pairs throughout and simple ambulacral plating with an enlarged tubercle on every third element. Smith, A. B. 2016. British Jurassic regular echinoids. Part 2 Calycina. Monographs of the Palaeontographical Society (no. 646), pp. 69-176, pls 42-82.