Sphenotrochus (Sphenotrochus) evexicostatus Cairns in Cairns & Keller, 1993

Fig. 15K, L

Sphenotrochus intermedius . - Macnae and Kalk 1958: 123.

Sphenotrochus sp. -Pichon 1974: 176, fig. 5.

Sphenotrochus aurantiacus . - Boshoff 1981: 38-39 (in part).

Sphenotrochus (Sphenotrochus) evexicostatus Cairns in Cairns & Keller, 1993: 255, 258, fig. 9A-H.

Type locality.

Off south-eastern Mozambique (RV 'Anton Bruun’ stn. 372B: 24°48'00"S, 34°59'00"E); 42 m (Cairns and Keller 1993).

Type material.

The holotype and five paratypes are deposited at the NMNH, whilst one paratype is deposited at the SAM (Cairns and Keller 1993).

Material examined.

ORI_DIIIi1 (3 specimens): Locality data unknown. SAMC_A090080 (3 specimens): Southern margin, 22 km from Cape Point / 4 km off Elsies Estuary, 34°09'59.99"S, 18°27'29.99"E; 24 m. SAMC_A090083 (1 specimen): Southern margin, 18 km from Cape Point / 16 km off Buffels Wes Estuary, 34°13'00.00"S, 18°35'00.0"E; 44 m. SAMC_A090085 (in part: 1 specimen): Locality data unknown; 43 m. SAM_H806 (8 specimens): Southern margin, 37 km from Port Elizabeth / 32 km off Bakens River Estuary, 34°05'29.99"S, 25°55'14.99"E; 20 m. SAM_H3200 (2 specimens): Eastern margin, 19 km from Shaka’s Rock / 3 km off Mdloti Estuary, 29°38'59.99"S, 31°07'59.99"E; 49 m. SAM_H3201 (1 specimen): Eastern margin, 19 km from Shaka’s Rock / 3 km off Mdloti Estuary, 29°38'59.99"S, 31°07'59.99"E; 71- 73 m. SAM_H3202 (10 specimens): Southern margin, 18 km from Gonubie /off Gqunube Estuary, 29°38'59.99"S, 31°07'59.99"E; 90 m. SAM_H4584 (1 paratype): Eastern margin, 31 km south of Ponta Do Ouro / 32 km off Kosi-Kumpungwini (Sifungwe) Estuary, 24°48'00"S, 34°59.00"E; 42 m. USNM 77188 (12 paratypes): Eastern margin, 24 km from Shaka’s Rock / 5 km off Mdlotane Estuary, 29°18'59.99"S, 31°21'00.00"E; 38 m.

Description.

Corallum cuneiform. Thecal faces diverge at 12°, producing a triangular profile in lateral view. Base rounded. Calice elliptical (GCD:LCD = 2.4-3.1), with serrated calicular margin. Largest specimen examined (SAM_H806) 6.7 × 2.3 mm in CD, and 8.8 mm in H, showing an episode of rejuvenescence. Costae rounded, equal in width, and do not overlap with adjacent costae. Costae slanting inwards towards base, being continuous until ~ 1.5 mm above base where they form discontinuous ridges. All costae smooth, except C1 and adjacent C4, which are slightly granulated. Pairs of C4 occur in each half-system adjacent to S1 (32 costae), but S4 do not correspond to C4. Intercostal striae wider than costae. Corallum white but sometimes light-yellow to brown.

Septa hexamerally arranged in three cycles according to the formula: S1-2> S3 (24 septa). S1-2 moderately exsert, equal in width, and join columella deep in fossa with slightly sinuous axial margin. S3 less exsert, 1/3 the width of S1-2, and bear slightly dentated axial margin. Columella solid and lamellar. Lamella rises almost to the height of septal upper margins. Columellar elements and septal faces bear low-profile granules.

Distribution.

Regional: Southern to eastern margin of South Africa, from off Cape Point extending towards Durban; 24-90 m. Elsewhere: Mozambique (Cairns and Keller 1993); Madagascar (?) Pichon 1974); 12-73 m.

Remarks.

Examined specimens of Sphenotrochus (S.) evexicostatus add no taxonomic knowledge to the existing diagnosis. The species is well described by Cairns and Keller (1993), who noted that it may co-exist with S. imbricaticostatus, which has similar septa, costae, and columella. However, S. evexicostatus can be distinguished in having: round, ridged, non-imbricate, equidistant costae; wide intercostal striae that are> 35% width of costae; and S3 ~ 1/3 the width of S1-2. The ornamentation of costae of S. evexicostatus, which is continuous from calice and become disconnected ~ 1.5 mm from base, is also a distinctive feature.