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ADDENDA. 



Species and Varieties of Trig onice figured in this Monograph which were not received 

 sufficiently early to allow of the descriptions being placed in their proper sectional 

 order. 



Trigonia scapha, Ag. PI. XXXVIII, fig. 6 (Scaphoide^;). 



Trigoxia scapha, Agassiz. Trigonies, p. 15, pi. vii, figs. 17 — 20, 1840 (internal 

 moulds). 



— — d'Orbigny. Prodrome de Paleont., vol. ii, p. 79, No. 293, 1850. 



— — Pictet. Paleont. Suisse, pi. cxxviii, figs. 6 — 8, 1866. 



— Hunstanton en sis, Seeley. On the Fossils of the Hunstanton Red Rock, 



Ann. and Mag. Nat. Hist., 3 series, No. 82, 

 p. 276, October, 1864 (mould). 



Shell scaphoidal , anterior side short, somewhat truncated, posterior side produced, 

 rather depressed ; umbones elevated, somewhat recurved, superior border lengthened, 

 nearly straight, curved posteally with the siphonal border, which is of moderate length, 

 its lower extremity curving elliptically with the lower border. The escutcheon is 

 moderately lengthened and depressed ; the area is wide and slightly convex. The only 

 specimen at my disposal is deprived of the test ; the area therefore exhibits only the muscle 

 scar ; the other portion of the shell or pallial surface retains traces of the surface ornaments ; 

 there are a few nearly perpendicular subnodose costae which pass downwards from the 

 angle of the valve to the middle, where they meet the extremities of another oblique 

 anteal series of similar but smaller costae. The dental hinge processes are large. 



Dimensions of the mould above described : 



Length, 26 lines ; height, 14 lines ; thickness, 9 lines. The convexity is less than in 

 the mould figured by Agassiz, which is probably the effect of vertical pressure. 



The only British specimen known is in the Woodwardian Museum : Cambridge, the 

 surface ornaments are obscure. It was deposited there by Mr. H. Seeley, and catalogued 

 by him in his list of Hunstanton fossils under the name of Trigonia Hunstantonensis, 

 'Ann. and Mag. Nat. Hist.,' October, 18G4. Subsequently in a communication to the 

 same periodical Mr. Seeley expressed his belief that the fossil was not derived from the 

 red rock of Hunstanton, but that it came from the drift of Norfolk. The general aspect of 

 the mould agrees with the latter conclusion. 



