TRIGONOARCA. 47 



Greensand, the apparent differences between the two forms being explained by 

 the imperfect state of preservation of the specimens from the Upper Greensand of 

 Devizes. A comparison of a number of examples from these and other localities 

 confirms the view of d'Orbigny. 



The specimens from the Gault are, on the average, of larger size than those 

 from the Blackdown Greensand, and, owing to their different mode of preserva- 

 tion, differ a little in appearance from the latter. The record of this species from 

 the Lower Greensand of Kent, given by Morris, is apparently erroneous. 



Types. — The types of both Area carinata and Cucullsea costellata are in the 

 British Museum. 



Distribution. — Greensand of Blackdown (zones viii to xii, especially x) and 

 Haldon. Upper Greensand of Devizes and Ventnor. Gault of Black Ven. Zones 

 of Acanthoceras mammilatum and Hoplites interruptus at Okeford Fitzpaine. Gault 

 (zones i, ii, viii — x) of Folkestone. Chalk Marl (zone of Schlcenbachia varians) of 

 Ventnor and Folkestone. 



Genus — Trigonoarca, T. A. Conrad, 1863. 



['Proe. Acad. Nat. Sci. Philad.' (1862), 1863, p. 289; ibid., 1872, p. 54; *Araer. Journ. Conch.,' 

 vol. iii (1867), p. 9; Appendix to W. C. Kerr's ' Eep. Geol. Surv. N. Carolina, vol. i, 1875 

 (Raleigh); figured, 'Journ. Acad. Nat. Sci. Philad.,' ser. 2, vol. iv (1860), p. 281, pi. xlvii, 

 fig. 20.] 



Tkigonoarca Passtana (d'Orbigny), 1844. Plate VIII, figs. 9 a— c, 10 a, b. 



1832. Cucullea caeinata, A. Passy (non Sowerby). Descript. Geolog. de la 

 Seine-Infer., p. 8 (of expl. of plates), pi. xiv, 

 figs. 11, 12. 

 1844. Arca Passtana, A. d'Orbigny. Pal. Franc. Terr. Cret., vol. iii, p 241, 



pi. cccxxvii, figs. 1, 2. 

 1850. — — — Prodr. de Pal., vol. ii, p. 164. 



1866. — — F. J. Pictet and G. Campiclie. Foss. du Terr. Cret. de 



Ste. Croix (Mater. Pal. Suisse, ser. 4), pt. 3, p. 475. 

 1871. — — F. Stoliczka. Palaeont. Indica, Cret. Fauna S. India, 



vol. iii, p. 343 {Trigonoarca). 

 1896. — ligeriensis, A. J. Jukes-Browne and W. Hill. Quart. Journ. Geo). 



Soc, vol. Hi, p. 153 (from Chard). 

 ? 1897. Cucur.LiEA Passtana, B. Leonhard. Die Fauna der Kreidef. in Ober- 

 schles. (Palaeontographica, vol. xliv), p. 51. 



Description. — Shell oblong, more or less elongate, convex, inequilateral, rather 

 short anteriorly. Ventral margin nearly straight, placed a little obliquely ; 



