J. S. GARDNER ON BRITISH CRETACEOUS NUCULIDA. 125 
NV. ovata and the other by NV. wmpressa, each type having ranged 
throughout the greater part of the Cretaceous period. Of these, 
the following have been met with in our area :— 
TypsE oF N. ovATA. 
NN. planata, Desh. Neocomian. 
NV. ovata, Mant. Gault. 
NN. capseeformis, Mich. Gault. 
NV. obtusa, Sby. Blackdown and Grey Chalk. 
Typr oF N. IMPRESSA. 
N. Cornueliana, d’Orb. Neocomian. 
NV. sumplew, Desh. Neocomian. 
NN. albensis, @Orb. Gault. 
N. umpressa, Sby. Blackdown and Grey Chalk. 
N. Meyert, Gardn. Neocomian. 
OvAT@ RETICULATA. 
The few species belonging to this group possess a reticulated 
structure and toothed margin. Only one is British. 
Subdivision OVATH LAVIGATA, 
Type oF N. ovata. 
Gault Species. 
Novctvtra ovata, Mantell. Plate III. figs. 1-3, Plate IV. figs. 28-30. 
Nucula ovata, Mantell, Geology of Sussex, pl. xix. figs. 26, 27 
(1822) (non ovata, d’Orb., Pal. Frang. vol. i. p. 173, pl. 302, 
figs. 1-3). It has been included, on imperfect data, in the genus 
Cucullella, M‘Coy. 
This shell averages, length 19 mm., breadth 10 mm., height 
16 mm.; but these dimensions are occasionally exceeded, attaining 
as much as 25 mm. in length, 12 mm. breadth, and 16 mm. height *. 
The form varies considerably, the anterior outline being subovate 
to subangulate, and even slightly produced into a blunt beak. The 
opposite end is more regularly ovate. The inferior margin is 
straight for some distance, slightly constricted opposite to the 
umbo and slightly sinuous towards its anterior termination near 
the lunule. The test is solid, and has a white and glossy ap- 
pearance ; it is strongly marked by lines of growth, which in very 
many specimens become deep furrows, especially numerous towards 
the inferior margin. There are no transverse ribs externally, though 
a radiating structure can always be seen in certain lights. In- 
ternally, the test is nacreous, the cast smooth, the adductor muscles 
not prominent, the denticles of the hinges very numerous and defined. 
* Tn the department of the Aube, in France, it is found in several places 
equalling IN. capseformis in size, and at St. Florentin it passes into that 
species. 
