Thylechinus (Orthechinus) quincuncialis Gregory, 1906

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 594

Thylechinus (Orthechinus) quincuncialis Gregory, 1906 ( Figs 8J, K; 9 E-G)

Thylechinus quincuncialis Gregory, 1906: 222 , pl. 11, fig. 8.

Thylechinus (Orthechinus) quincuncialis – Abdelhamid 1997: 143, fig. 5 (4).

MATERIAL EXAMINED. — 50 specimens from the Turonian of Wadi Abu Qaada (Wata Formation), AS- UAQE 20-69, Wadi Abu Qaada echinoid horizon 2 ( QEH 2).

MEASUREMENTS. — See Table 6.

DESCRIPTION

Test size variable. Adapical surface slightly convex. Poriferous zones uniserial. Ambulacral tubercles are as large as interambulacral tubercles but rapidly reduced in size near apical disc. Major ambulacral plates are composed of triads arranged in diadematoid manner ( Fig. 9F, G ), whereas near apical disc, they are composed of triads of simple plates. Interambulacral area with two columns of imperforate, crenulated primary tubercles. In small- and medium-sized specimens extrascrobicular surface is occupied by large granules lying on the upper right and upper left of each ambital plate. As the size of test increases, there are two external columns of secondary tubercle are confined to the ambital area. In the large specimens (diameter more than 30 mm), there are two external and two internal columns of secondary tubercles; they are nearly as large as the primary tubercles ( Fig. 9E ). The adapical suture of interambulacral plates in small to mediumsized individuals is slightly concaved upwards. Maximum concavity is attained in specimens more than 30 mm diameter ( Fig. 9E ). Peristome faintly depressed.

REMARKS

This species is distinguished from Thylechinus (Thylechinus) sinaiensis n. sp. in having more than two columns of tubercles on each interambulacrum.

Figures

FIG. 9. — Camera lucida drawings: A, plating, tuberculation and poring of subambital ambulacrum in Phymosoma thevestense (Péron & Gauthier, 1879) from the Coniacian-Santonian of Abu Roash; B-D, plating, tuberculation and poring in Thylechinus (T.) sinaiensis n. sp. from the Turonian of Wadi Abu Qaada; B, adapical ambulacrum; C, ambital ambulacral plates; D, subambital interambulacral plates; E-G, plating, tuberculation and poring in Thylechinus (O.) quincuncialis Gregory, 1906 from the Turonian of Wadi Abu Qaada; E, ambital interambulacral plate; F, adapical ambulacrum; G, ambital ambulacrum. Scale bars: A, B, 0.5 mm; C, 0.4 mm; D, 0.8 mm; E, 2 mm; F, 0.9 mm; G, 1 mm.