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Milnia Haime, 1849, p. 217

[=Thylosalenia Pomel, 1883, type species Hemicidaris patella Agassiz, 1840, by original designation ]

Diagnostic Features
  • Periproct displaced towards posterior along anterior-posterior axis.
  • Apical disc not raised above the corona; smooth.
  • Plating variable; usually with one large suranal plate plus smaller ones posteriorly.
  • Posterior genital plate strongly U-shaped; bounded by posterior ocular plates, genital plate 5 and suranal plates.
  • Ambulacral plating trigeminate throughout; granulation developed between the two columns of primary tubercles.
  • Pore-pairs uniserial to the peristome; no phyllode development
  • All tubercles perforate and crenulate.
  • Peristome rather deeply invaginated.
Distribution
Middle Jurassic (Callovian) to Lower Cretaceous (Valanginian); Europe.
Name gender feminine
Type
 Milnia decorata Haime, 1849 [=Acrosalenia angularis Agassiz, in Agassiz & Desor,1847], by original designation.
Species Included
  • M. angularis (Agassiz, in Agassiz & Desor, 1847); Oxfordian-Kimmeridgian, Europe.
  • M. guittoni Vadet, Nicolleau & Pineau, 1996; Callovian, France.
  • M. patella (Agassiz, 1846); Valanginian, Europe.
Classification and/or Status

Calycina, Salenioida (stem group)

Presumed monophyletic.
Remarks
Differs from Acrosalenia in having a slightly stronger posterior elongation of the apical disc opening and a more slender and much more strongly U-shaped posterior genital plate. Haime established this genus on the specimen illustrated here. As Wright (1856) documented, this was very quickly treatred as a synonym of Acrosalenia.

Pseudomilnia has a very similar test appearance, but has strongly developed phyllodes, whereas in Milnia the pore-pairs remain uniserial to the peristome edge.

Haime, J. 1849. Observations sur le Milnia decorata. Annales des Sciences naturelles, (3) 12, 217-240.

Smith, A. B. 2016. British Cretaceous regular echinoids. Part 2 Carinacea. Monographs of the Palaeontographical Society (no. 646), pp. 69-176, pls 42-82.
Wright, T. 1857-1878.  Monograph of the British fossil Echinodermata of the Oolitic Formations: Volume 1. The Echinoidea.  Palaeontographical Society Monographs, London. i-xviii + 1-371, pls 1-80. 1-154, pls 1-10 (1857); 155-302, pls 11-22 (1858); 303-390, pls 23-36 (1859); 391-468, pls 37-43 (1861); 469-481 (1878).