AND MOLLUSCA FROM ANGOLA, PORTUGUESE WEST AFRICA. 565 



related to Exqgyra fiabellata of Goldfuss, although the umbonal region is entirely 

 absent. The lower valve consists of a fairly well-arched portion of possibly the 

 ventral region, which is furnished with remains of seven obtusely angulate, 

 equidistant radial costse divided by wide sulcations which are ornamented with 

 robust, concentric and regularly undulating ridges and striations, these being 

 continued over the summits of the costse. The opposing surface representing part 

 of the upper or flatter valve, which fits closely into the other, exhibits five radial, 

 funnel-shaped, roundly convex, and smooth plications separated by moderately 

 narrow and deep grooves. For an explanation of these structures it is necessary to 

 refer to good figures such as those published by Orbigny of examples from the 

 French Cenomanian. _0n that author's plate (475) the details similar to those in 

 the Angola fossil are more or less well represented. The strongly developed, funnel- 

 shaped costse of the upper valve are well seen in his fig. 1, whereas the more 

 obtusely angulate character of the costse of the lower valve with their wide 

 dividing furrows are to be observed in fig. 2. 



Under the same name (Ostrea cf. fiabellata), but without description or figure, 

 M. Choffat * has recognised a probably similar mollusc in the Cenomanian-Turonian 

 beds of Dombe Grande, Angola. 



It is interesting to note that the double plication of this species of Exogyra was 

 used by Bayle as the significant character for the establishment of his genus 

 Ceratostreon, the true Exogyra having only its lower valve plicated, while the 

 upper bears a concentric sculpture. This fossil measures 50 by 49 mm., its greatest 

 diameter being 20 mm. 



Distribution. — This species has a wide geographical range, being found in Europe 

 (France, Italy, Portugal, etc.), Algeria, Egypt, Tunisia, Arabia, Palestine, etc. It is 

 essentially Cenomanian, and chiefly belongs to the upper part of that horizon, as well as 

 occurring in the Lower Turonian rocks of the island of Socotra, according to Kossmat. 



Occurrence. — The fossil is without matrix, except as an infilling material between- 

 the valves, composed of a hard light-coloured limestone. 



Locality. — No. 12 — Hanha near Lobito. 



Fam. Pectinid^e. 

 Neithea tequicostata, Lamarck. (PL I, figs. 2 and 3.) 



Pecten xquicostatus, Lamarck : Hist. Nat. Anim. sans Vert., 1819, vol. vi, part 1, p. 181. 

 Vola xquicostata, Choffat: Recueil Etudes Pal. Faune Cret. Portugal, 1901-02, pi. iii, fig. 10, p 152. 

 Pecten (Neithea) xquicosta/us, Pervinquiere : Etudes Pal. Tunisienne: Gast. Lamellib. Terr. Crstaces, 1912, 

 p. 135 



Remarks. — A somewhat small lower valve exhibiting an external view is referred 

 to this species. The length and height are the same, viz. 16 mm. It is furnished 



* Mem. Soc. Phys. Hist. Nat. Geneve, 1888, vol. xxx, No. 2, p. 25 ; Contrib. Ge'ol. Colonies Portugaises Afrique, 

 1905, part 2, p. 59. 



