The Echinoid Directory

• Test small (less than 20 mm diameter), flattened above and below.
• Apical disc hemicyclic, the posterior two ocular plates exsert. Genital plates rather short and wide, without tubercles; gonopores towards interradial point. Ocular plates smaller than genitals, hexagonal. Periproct rather large and circular; possibly with valve like plates (reported by Mortensen); no perianal tuberculation.
• Ambulacra straight, expanding to ambitus; aboral pore-pairs uniserial, non-conjugate; plating simple without differentiated primary tubercles close to apex, but with small primary tubercle present elsewhere intersperced with pustular ornament; plating trigeminate in acrosaleniid style. Adoral ambulacral plating trigeminate with a large primary tubercle. Primary tubercles largest at ambitus. Pore zones expand adorally to form short phyllodes.
• Interambulacra a little wider than ambulacra. Each with a large primary tubercle; tubercles largest at ambitus, decreasing in size adapically and adorally. Rather wide interradial zone from ambitus adapically that, in its lower part, has numerous granules, but which is rather bare adapically.
• Primary tubercles with large imperforate mamelon and no platform. Ambulacral and interambulacral tubercles similar in size.
• Peristome subpentagonal, large (a little over half test diameter). Buccal notches shallow and broad with distinct lip; no obvious basicoronal plate.
• Spines unknown.

Atopechinus cellensis Thiery, 1928, p. 100, by monotypy.

• A. cellensis Thiery, 1928; Bathonian, France.
• A. minuta (Mortensen & Mercier, 1939); Toarcian, France, England.

Euechinoidea, Echinacea, Arbacioida, Glypticidae.

The type was redescribed and figured by Mortensen (1935). Vadet (1995) provided more information based on a second specimen (illustrated here). Panglypticus Lambert & Thiery, 1914, is very similar, differing primarily in having a smaller periproct and larger, more pentagonal genital plates. Close in appearance to Prototiara but distinguished from that taxon by having well developed primary ambulacral tubercles beneath the ambitus.

Mortensen, T. 1935. A monograph of the Echinoidea II. Bothriocidaroida, Melonechinoida, Lepidocentroida and Stirodonta. C. A. Reitzel, Copenhagen.

Thiery, J. 1928. Note sur quelques echinides de la region de la Voulte (Ardeche). Travaux de la Laboratoire geologique, Faculte des Sciences Lyon 13 (2), 81-103, 1 pl.

Vadet, A. 1995. Un echinide rare, Atopechinus cellensis dans le Bathonien du Ravin du Chenier. Memoires de la Societe academique du Boulonnais 16, 116.