10 



. 9 mm, 



7 



• 6 „ 



4-75 



• 4-5 „ 



24 CRETACEOUS LAMELLIBRANCHIA. 



very near the posterior end. Lunule elongate, much depressed, sharply limited. 

 Surface with lines of growth. Margins entire. Anterior part of hinge-line with 

 about eighteen teeth, posterior part with seven. 



Measurements : 



(i) (2) (3) 



Length . . . 13-5 . 11-5 . 11 



Height . . .10 .8-5.8 

 Thickness . . — . — . 5'5 



Affinities. — This species is distinguished from N. obtusa, Sowerby, and N. ovata, 

 Mantell, by the sharply defined lunule and the angular posterior extremity; it is 

 also a smaller form. 



N. apiculata, Sowerby (Plate IV, fig. 8), from Blackdown, appears to me 

 to be only a variety of N. impressa ; it is somewhat shorter in proportion to its 

 height than the ordinary forms of N. impressa, and consequently has a more 

 rounded outline. Sowerby's diagnosis of N. apiculata is " Convex, smooth, trans- 

 versely obovate; posterior extremity pointed." A specimen in the Museum of 

 the Geological Society of London (No. 1564, Fitton Collection) is, I believe, the 

 type, but is a little smaller than Sowerby's figure. The only other example known 

 to me is in Mr. Meyer's Collection. The late Rev. W. Downes 1 considered iV. 

 apiculata to be a synonym of N. antiquata t Sowerby; but that species is more 

 triangular in outline, the valves are much more convex, and the umbones more 

 prominent. 



Types. — One of the types (Sowert^'s lower figure) is in the British Museum. 

 One of the specimens figured by Gardner (fig. 12) is in the Bristol Museum ; I 

 have not seen the others ; they are stated to be in the Rev. W. Downes' Collection, 

 now in the Exeter Museum. 



Distribution. — Blackdown Greensand. 



Nucula albensis, iVOrbigny, 1844. Plate IV, figs. 9 a, b, 10, 11, 12 a, b, 13 a, b, 



14 a, b, 15 a, b, 16, P 17. 



Is! I. Nucula albensis, A. d'Orbigny. Pal. Franc. Terr. Cret., vol. iii, p. 172, 



pi. ccci, figs. 15 — 17. 

 1850. — — Prodr. de Pal., vol. ii, p. 137. 



L866. — F. J. Pictet and G. Campiche. Foss. du Terr. Cret. de 



Ste. Croix (Mater. Pal. Suisse, ser. 4),pt. 3, pp. 411, 

 417, pi. cxxix, fig. 11. 

 1 ss I . — — J. S. Gardner. Quart. Journ. Geol. Soe., vol. xl, p. 128, 



pi. iii, figs. 6—8 ; pi. iv, figs. 24, 25. 



1 'trans. Dev. Assoc, ' vol. xii (1880), p. 436; and 'Quart. Journ. Geol. Soc.,' vol. xxxviii 

 (1882), p. 88. 



