. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. LOWER CRETACEOUS AMMONITES FROM ANGOLA 303. Fig. 27. Oxytropidoceras (Mirapelia) buarquianum (White). The suture line, somewhat simplified by erosion, of SAM-PCA2693, a douglasi morphotype. Approx. X 2. There are 13-20 ribs per half whorl. A somewhat eroded suture-line is shown as Figure 27. O. buarquianum morphotypes are insensibly connected to O. douglasi morphotypes (Fig. 3A-B). Typically (Fig. 25A-B), this morphotype is strongly compressed, with 22-32 broad, low, weak ribs per whorl, and an indis
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. LOWER CRETACEOUS AMMONITES FROM ANGOLA 303. Fig. 27. Oxytropidoceras (Mirapelia) buarquianum (White). The suture line, somewhat simplified by erosion, of SAM-PCA2693, a douglasi morphotype. Approx. X 2. There are 13-20 ribs per half whorl. A somewhat eroded suture-line is shown as Figure 27. O. buarquianum morphotypes are insensibly connected to O. douglasi morphotypes (Fig. 3A-B). Typically (Fig. 25A-B), this morphotype is strongly compressed, with 22-32 broad, low, weak ribs per whorl, and an indistinct umbilical wall. It is perhaps worth noting that it is a 'law' of polytypic ammonite species that the compressed variants are weakly ornamented, and that strength of ornament increases with inflation. Two examples, SAM-PC A 3603-3604, show the rather dense, straight ribs of O. salasi Young, becoming projected near the venter (Fig. 19D-E), and are connected by intermediates to O. douglasi. These O. salasi variants show a low umbilical wall, broad convex flanks and a lanceolate whorl section, and were clearly rather evolute. Although the siphonal keel is not preserved, it certainly stood well above the venter. The dense, narrow, simple ribs are distinctly prorsiradiate and only very slightly flexuous, with at least twenty-two ribs per half whorl. The ribs swell slightly at the ventrolateral shoulders and curve strongly forward to meet the siphonal keel. Discussion The Angolan material shows an insensible transition between O. buarquia- num (White) and O. douglasi Knetchel and they are synonyms. It is unfortun- ate that White's (1887) species has priority because the O. douglasi morpho- types predominate. There is little to separate O. packardi Anderson from the O. douglasi morphotypes and it should also fall into synonymy. Several of the Angolan morphotypes are extremely close to O. mirapelianum, which is a broadly contemporaneous European species. However, until the populat
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
