NUCULA. 
nw 
or 
Description.—Shell subtriangular or more or less oval, compressed ; posterior 
part very short and somewhat angular; anterior part usually tapering rapidly, 
with the extremity rounded. Ventral margin curved evenly. Antero-dorsal 
margin curved ; postero-dorsal nearly straight or slightly concave. Umbones not 
prominent, curved. Lunule shallow, cordate, often not sharply defined. Anterior 
area limited by a faint ridge. Surface smooth, but with lines of growth. Margin 
smooth. Adductor impressions shallow. 
Measurements : 
(1) (2) (3) (4) (5) 
Length . ; Meee, «teen. l4d. 0 A mme 
Height. : Pwiowee eta . LS fo, 10 « ODE e 
Thickness : — i. Ow FO — 
; : 7 
Affinities. —N. Timotheana, Pictet and Roux,’ is shorter, and apparently more 
compressed than is N. albensis; N. ovata, Mantell, is less compressed and more 
rounded in outline; N. dimpressa, Sowerby, is more oval, and has a more depressed 
and better defined lunule. 
Remarls—This species varies considerably in the proportions of length and 
height—the shorter examples being more triangular, the longer more oval in out- 
line. A form found in the Blackdown Greensand (Plate IV, fig. 17), of which 
I have seen only a few specimens, approaches very closely the shorter types of 
N. albensis, but I have not sufficient material to allow me to speak of its affinities 
with certainty. 
Types.—I have not seen the type; it appears to be missing from the d’Orbigny 
Collection in the Museum of Natural History, Paris. Some of the specimens 
figured by Gardner (figs. 6—8) are in the British Museum. 
Distribution.—Lower Gault (zone vi) of Folkestone; Gault of Black Ven; 
Cambridge Greensand (derived). ? Grey Chalk (jide Gardner). 
Noucuna GauLrina, Gardner, 1884. Plate IV, figs. 18 a—c, 19, 20, 21 a—e. 
1884. Nucuna gavtrina, J. S. Gardner. Quart. Journ. Geol. Soe., vol. xl, 
p. 184, pl. iii, figs. 9—11, 26, 27. 
Description.—Shell small, triangular, rather convex; pointed anteriorly and 
posteriorly. Ventral and antero-dorsal margins gently curved ; postero-dorsal 
margin slightly concave. Umbones pointed, curved, placed very posteriorly. 
Lunule cordate, sharply defined. Anterior area bounded by a ridge passing from 
the umbo to the anterior extremity. Surface nearly smooth, but with lines of 
' Moll. Foss. Gres verts de Genéve (1852), p. 476, pl. xxvix, fi 
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