NUCULA. 23 



Description. — Shell oval or ovate-oblong, moderately convex, rounded an- 

 teriorly and posteriorly ; ventral margin evenly curved. Umbones not prominent, 

 placed posteriorly. Lunule indistinctly denned. Surface smooth, but with growth- 

 lines. Hinge with numerous small teeth — about eighteen on the anterior part, 

 and nine on the posterior, — the two parts forming an obtuse angle (about 133°). 



Measurements : (i) (2) 



Length .... 21 .. 20 mm. 



Height . . . .13 . . 14 „ 

 Thickness . . .13 . . — „ 



Affinities. — N. obtusa is closely allied to N. ovata, Mantell; it differs from the 

 latter (1) in being more oval, (2) in having the ventral margin more regularly 

 curved, (3) in the umbones being usually placed more posteriorly, (4) in the 

 absence of a constriction near the ventral margin, and (5) in the indistinct lunule. 

 Types. — The type is in the Bristol Museum. The specimen figured by 

 Gardner is in the Museum of Practical Geology, Jermyn Street. 



Distribution. — Blackdown Greensand (zones vii to x) ; Greensand of Haldon 

 (fide Downes) ; Upper Greensand of Devizes and Warminster. 



Nucula impressa, 8oiverby y 1824. Plate IV, figs. 5, 6 a — c, 7,? 8 a, b. 



1824. Nucula ihpbessa, J. de C. Sowerby. Min. Conch., vol. v, p. 118, pi. 



cccclxxv, fig. 3. 

 ? 1836. — apiculata, J. de C. Sowerby. Trans. Geol. Soc, ser. 2, vol. iv, 



p. 3-12, pi. xvii, fig. 10. 

 1850. — impressa, A. d'Orligny. Prodr. de Pal., vol. ii, p. 163. 

 1854. — — J. Morris. Cat. Brit. Poss., ed. 2, p. 217. 



? 1854. — apiculata, Morris. Ibid., p. 217. 

 1866. — impressa, F. J. Pictet and G. Campicke. Poss. du Terr. Cret. de 

 Ste. Croix (Mater. Pal. Suisse, ser. 4), pt. 3, p. 418, 

 pi. cxxix, fig. 16. 

 1884. — — J. S. Gardner. Quart. Jouru. Geol. Soc, vol. xl, 



p. 128, pi. iv, figs. 9—12. 



Non 1846. Nucula impressa, A. E. Beuss. Die Verstein. der bohm. Kreideformat, 



pt. 2, p. 6, pi. xxxiv, figs. 6, 7. 



— 1867. — — E. Gucranger. Album Paleout. du Dep. de la Sarthe, 



p. 15, pi. xx, fig. 16. 



— 1897. — — A. Fritscli. Stud, im Gebiete der bohm. Kreideformat. 



vi. Die Chloraeker Schichten, p. 56, 

 fig. 61. 



Description. — Shell oval, rounded anteriorly, angular posteriorly ; ventral 

 margin evenly curved, postero-dorsal margin slightly concave. Umbones placed 



