AND MOLLUSCA FROM ANGOLA, PORTUGUESE WEST AFRICA. 571 



The fossil is closely related to Area diceras of Seguenza, from the Cenomanian of 

 Italy, which was founded on a similar limestone cast, and chiefly seems to differ in " 

 its rather greater length of valve, the dimensions of the type showing a length of 

 60, height 45, and diameter 50 mm. 



Distribution. — This species belongs to the Cenomanian of Italy and Tunisia, and 

 is also found in Algeria, according to Pervinquiere. 



Occurrence. — The specimen was found associated with some fragmentary ammon- 

 ites of the group of Schloenbachia injiata, and some other mollusca. 



Locality.— No. 294— Plateau 800 feet E. of Lobito. 



Fam. TRiGONiiDiE. 



Trigonia crenulata, Lamarck. (PI. I, fig. 14.) 



Trigonia crenulata, Lamarck: Hist. Nat. Anim. sans Vert., 1819, vol. vi, part 1, p. 63 ; Orbigny, Pal. 

 Francaise: Terr. Cretaces Lamellibranchia, 1843, vol. iii, pi. 295, p. 151 ; Coquand, Geol. Pal. 

 Constantine, 1862, p. 290. 



Remar'ks. — -A small limestone cast with both valves closed together agrees in 

 every particular with specimens of this species in a similar condition from the 

 Cenomanian of France (Rouen), in the British Museum. It shows a well-excavated 

 areal region, while the sides of the valves retain obscure evidence of the obliquely 

 arranged costse. 



Dimensions. — 



Length ...... 25 mm. 



Height . . ... . . 20 ,, 



Diameter . . . . . 17 ,, 



A better specimen of what is apparently the same species is preserved as an 

 impression on a limestone slab, from Catumbella, Angola, belonging to the British 

 Museum (Ansorge collection). A wax squeeze of this yields an externo-lateral 

 view of a fragmentary right valve .in which the antero-marginal region is not 

 present. It shows, however, a sharply defined posterior carina to which is con- 

 nected anteriorly a regular series of equidistant coarsely crenulated costse, much 

 finer costse of similar but more minute structure being present on an incomplete 

 postero-areal surface. 



Great resemblance may be noted between this specimen and Trigonia sub- 

 crenulata as figured by C. A. White* from the Schloenbachia injiata zone of 

 Brazil (province of Sergipe), which is much more likely to represent a form of 

 T. crenulata rather than T. subcrenulata described by Orbigny t from the Aptian 

 rocks of Columbia, South America, which has fewer and more distinct costse, besides 

 belonging to an older Cretaceous horizon. 



Distribution. — This species was originally described from Mans in the north- 



* " Contributions to the Paleontology of Brazil," Archiv Mus. Nacion. Brazil, 1888, vol. vii, pi. v, fig. 3, p. 70. 

 t Voyage dans I'Ame'rique Me'ridionale, pt. 4, " Paleontologie," 1842, vol. iii, pi. xix, figs. 7-9, p. 87. 



