The Echinoid Directory

Dixieus Cooke, 1948, p. 606

Diagnostic Features	Test large, ambitus below mid-height, depressed above and below. Apical disc small, less than a quarter of the test diameter; pentagonal in outline. Almost monocyclic, with ocular plates II and III barely reaching or only just excluded from the periproct. Periproct rather angular around anterior margin. Ambulacra straight; plating polygeminate (10-12 elements to a plate aborally, 5-6 elements to a plate adorally), compounded in phymosomatid style. Pore-pairs undifferentiated; biserial from ambitus to apex forming a rather broad irregular band. No phyllodes; pore zones weakly arced on adorally surface but not crowded towards the peristome. A single primary tubercle to each compound plate; positioned close to pore-pairs. Perradial zone moderately broad, with small secondary tubercle and granules. Interambulacral plates wider than tall; with a single primary tubercle, positioned centrally. Broad, slightly sunken aboral interradial naked zone present. Tubercles imperforate and strongly crenulate. Peristome small (but larger than the apical disc), circular, distinctly sunken, with clearly defined buccal notches with thickened lip; no tag. Spines and lantern unknown.
Distribution	Eocene, Southern USA, Caribbean.
Name gender	masculine
Type	Phymosoma dixiei Cooke, 1941, p. 17, by original designation.
Classification and/or Status	Euechinoidea, Phymosomatoida, Phymosomatidae. Subjective junior synonym of Acanthechinus Duncan & Sladen,1882.
Remarks	Resembles Actinophyma but is distinguished from that taxon by its smaller apical disc, smaller primary tubercles that do not have obviously incised areoles, and by its larger, more numerous flanking adradial tubercles. Nardinechinus has two or three equal tubercles on ambital and supra-ambital plates. Pliocyphosoma has almost identical tuberculation, but differs in having five-geminate plating throughout, not the 10 or more elements to a plate seen aborally in Dixieus. Cooke, C, W. 1948. Arbia and Dixieus, two new genera of echinoids. Journal of Paleontology, 22, 606-607. Cooke, C. W. 1959. Cenozoic echinoids of Eastern United States. United States Geological Survey Professional Papers 321, 1-106, 43 pls.