Mecaster roachensis (Gauthier, 1900) Mohamed Abdelhamid & Moustafa Azab, 2012

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 608

Mecaster roachensis (Gauthier, 1900) n. comb. ( Fig. 15O)

Periaster roachensis Gauthier in Fourtau, 1900: 24, pl. 1, figs 13-15. — Abdelhamid 1997: 156, fig. 7 (9, 10).

MATERIAL EXAMINED. — Two well preserved and numerous incomplete specimens from Abu Roash: Turonian (rudist unit), ASUARE152, Abu Roash echinoid horizon 1 ( REH 1) and the Coniacian-Santonian (Ostrea and Plicatula unit), ASUARE153, Abu Roash echinoid horizon 4 ( REH 4).

DESCRIPTION

Test size variable (L = 14.5-40.0mm) but mostly has large size. Outline heat-shape (W/L = 0.91-0.95).

Anterior margin with a marked sulcus. Adapical surface sloped forwards. Maximum height lies directly behind apical disc (H/L = 0.62-0.70). Posterior surface with oblique to nearly vertical truncation. Adoral surface swollen at the plastron. Sternal plates are approximately equal. Apical disc semi-ethmolytic, centric, and transverse. Frontal ambulacrum nonpetaloid (NIII = 40), deep, wider than the paired petals and conspicuously notching the ambitus until the peristome. Paired ambulacra petaloid, deep, and relatively narrow. Anterior paired petals long (LII = 7.8-13.9 mm, NII = 30- 45). Posterior paired petals shorter (LI/LII = 0.80, NI = 30-45), narrower, and less divergent than the anterior paired petals.

REMARKS

This species has fairly long, slightly depressed paired petals. The posterior pair is relatively shallower and shorter than the anterior one. The apical disc is semi-ethmolytic (the madreporite separates the genital plates 1 and 4). Fascioles are a narrow band of peripetalous ortho- to parafasciole sensu Néraudeau et al. (1998) and a narrow band of lateroanal parafasciole (bifasciata stage). The labrum is triangular and long. The sternal plates are nearly symmetric. As discussed in the previous species, regards the relation between the two genera Periaster, d’Orbigny, 1853 and Mecaster , the characters of the present species attribute it to the genus Mecaster . Mecaster roachensis n. comb. is distinguished from Mecaster fourneli in having lateroanal parafascioles, maximum width lies at the mid distance between anterior and posterior of test, more centric apical disc, and wider frontal ambulacrum.