. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. UPPERMOST CENOMANIAN-BASAL TURONIAN AMMONITES FROM SALINAS, ANGOLA 59. Fig. 5. Tetragonites sp. nov. ? aff. blaisoni Collignon. Whorl section of SAM-PCA2818. x 1. difference in whorl-section, the Angolan example can only be regarded as a closely allied, but different, species. Tetragonites rectangularis ampakabensis Collignon, from the Lower Ceno- manian of Madagascar, differs in being more involute (U=20-23% of diameter), somewhat more depressed, and with steeper umbilical walls. Tetragonites blaiso
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. UPPERMOST CENOMANIAN-BASAL TURONIAN AMMONITES FROM SALINAS, ANGOLA 59. Fig. 5. Tetragonites sp. nov. ? aff. blaisoni Collignon. Whorl section of SAM-PCA2818. x 1. difference in whorl-section, the Angolan example can only be regarded as a closely allied, but different, species. Tetragonites rectangularis ampakabensis Collignon, from the Lower Ceno- manian of Madagascar, differs in being more involute (U=20-23% of diameter), somewhat more depressed, and with steeper umbilical walls. Tetragonites blaisoni Collignon has similar relative proportions to the Salinas example, while the con- figuration of the constrictions is also closely comparable. It differs, however, in having much steeper umbilical walls and in being a Lower Cenomanian form. According to the amended diagnosis of Tetragonites glabrum Jimbo given by Matsumoto (1942&: 671), this species has a small umbilicus (20-26% of diameter), with slightly depressed whorls. The flanks converge to a rounded venter, while constrictions are few and irregular in development. Tetragonites epigonum (Kossmat) has an almost square whorl section (Usher 1952: 55), with not more than three prorsiradiate constrictions per whorl which appear to be effaced across the venter. Tetragonites jurinianus (Pictet) lacks constrictions at all growth stages, while in T. nautiloides (Pictet) constrictions are present only at diameters of less than 10 mm. The Angolan specimen is the only example of a Tetragonites yet recorded from uppermost Cenomanian strata, and in view of the slight, but distinct, differences from all previously recorded species of this genus, it probably merits a new specific name. The author hesitates to do so, however, due to the poor preservation of the unique Angolan example. Family Gaudryceratidae Spath, 1927 Discussion The family Gaudryceratidae has been subdivided into a number of sub- families—Gaudryceratinae (Spath 1
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