42 
Transactions of the Royal Society of South Africa. 
Trigonia cf. scABRA, Lamarck. 
Plate v., figs. 5-9. 
Trigonia, Bruguiere, Encyclop. Meth., 1797, pi. 237, fig. 1. 
Trigonia scabra, Lamarck, Hist. Nat. Anim. sans Vert., 1819, vol. 6, 
part 1, p. 63 ; Brongniart, Desc. Geol. Env. Paris, 3rd ed., 1822, 
pi. 9, fig. 5, p. 97 ; Deshayes, Desc. Coq. Caract. Terrains, 1831, 
pi. 13, figs. 4, 5, p. 35, 
Liriodon scaber, Bronn, Lethgea Geognostica, Versteinerungen, 1838, 
vol. 2, pi. 32, fig. 13, p. 702. 
Trigonia scabra, Agassiz, Etudes Grit. Moll. Foss. Mem. sur les 
Tri gonies, 1840, pi. 10, figs. 1-5, p. 28 ; Orbigny, Pal. Frangaise, 
Terr. Cretaces, Lamellibranchia, 1844, pi. 296, p. 153 ; Coquand, 
Geologie Paleont. Constantine, 1862, p. 299 ; Zittel, Denkschr. 
K. Akad. Wiss., 1864, vol. 24, pi. 9, fig. 2, p. 161 ; Stoliczka, 
Cret. Pelecypoda, Southern India, Pal. Indtca, 1871, pi. 15, 
figs. 24-26, pi. 16, figs. 35-40, p. 314; Segnenzn, Atti B. Accad. 
Lined (Eoma), 1882, p. 154. 
Description. — The specimens referred to as related to this species 
are of medium size, consisting of two right valves and a left 
one belonging to different individuals. The right valves exhibit 
some interesting structural characters which may be thus referred 
to. The anterior or pallial surface is covered with about 26 
well-elevated, sub-angulate costse, the summits of which are 
covered with obtusely spinulose tuberculations, the interspaces and 
lateral surfaces of the costae being ornamented with fine striations. 
The costae are obliquely disposed, equally divided at their termina- 
tions but widest anteriorly ; the posterior region is well excavated, 
margined in front by a fine carination, succeeding which occurs a 
depressed medianly sulcated area with its upper part decorated with 
minutely tubercled, closely arranged, short, oblique plications, the 
surface afterwards becoming smooth to the postero-ventral angle ; 
a lanceolate escutcheon follows the area, coarsely tubercled and 
obscurely striated transversely. 
Dimensions (right valve). — 
Length 32 mm. 
Height 30 „ 
Diameter 11 ,, 
Observations. — This Trigonia is closely related both to T. scabra 
and T. aliformis of Parkinson, and chiefly seems to differ from the 
latter in its more delicate costal structure and in the costae exhibiting 
a spinulose ornamentation rather than a funiculate and annulate 
character. The pallial costae also are of one distinct order throughout, 
