Rachiosoma rectilineatum (Péron & Gauthier, 1881)

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 590-592

Rachiosoma rectilineatum (Péron & Gauthier, 1881) ( Fig. 8G)

Cyphosoma rectilineatum Péron & Gauthier in Cotteau, Péron & Gauthier, 1881: 104, pl. 7, figs 1-4.

Rachiosoma rectilineatum – Geys 1992: 147, pl. 2, figs 8-9. — El Qot 2010: 272, pl. IV, figs 2a, b, 4, 5, text-fig. 5b.

MATERIAL EXAMINED. — 13 measured specimens and many non-measured ones from the Coniacian-Santonian (Matulla Formation) of Wadi Dakhl, ASUDLE2-14, Wadi Dakhl echinoid horizon 3 ( DEH 3).

MEASUREMENTS. — See Table 4.

DESCRIPTION

Adapical surface convex. Adoral surface feebly depressed around peristome. Ambulacral areas relatively wide, narrowed near apical disc. Poriferous zones uniserial, straight. Major ambulacral plates quadrigeminate, but trigeminate on adoral surface. Interradial extrascrobicular surface narrow. Adradial extrascrobicular surface relatively wide and occupied by very small tubercles lying near adradial suture, beside numerous granules.

REMARKS This species is known from the Santonian of Algeria, Egypt and Jordan. Geys (1992) recorded it from the basal part of the Turonian in Wadi Qena, Egypt.