J. 8S. GARDNER ON BRITISH CRETACEOUS NUCULIDA. 143 
that WV. capseformis rather leans towards Leda. Of the “ Angu- 
latee,” NV. pectinata seems to have no living representative; but 
N. bivirgata, with its beautiful sculpture, is allied to WV. msignis of 
Gould, and WV. gawltina to NV. sulcata of Bronn. Among the Lede 
he considers LZ. phaseolina to be allied to L. abyssicola of M. Sars, 
L. Marie to L. fragilis of Chemnitz, and L. solea to L. cuspidata of 
Philippi. The result of his examination of these and other groups 
of Gault fossils has led him to believe that the depth of the sea in 
which the Lower Gault of Folkestone was deposited was somewhere 
between 50 and 100 fathoms, though some of the smaller bivalves, 
especially belonging to other genera, are now inhabitants of much 
_ greater depths. 
The accompanying list is arranged in the manner which, I take it, 
is the most useful to those desirous of naming specimens; and as it 
is as complete as the material will allow to the present date, it 
would be convenient were no other names attached to specimens 
unless they present clearly marked characters different from those 
described. If read vertically, the lists are separately complete for 
each of the three stages of the Cretaceous system in Britain; and if 
horizontally, the representative species, or the lines of descent of 
each, can be traced through the three stages. 
Nucvna. Neocomian. Gault. Upper Greensand 
Group 1. Ovatz. and Grey Chalk. 
Ovate levigate. . 
Type “ovata.” N. planata. . ovata. 
N. capseeformis. He ONE 
Type “¢mpressa. ni eee a N. albensis. N. impressa. 
N. Meyeri. 
DORE T AGE ee EEC ee N. arduennensis. 
, var. pumila. 
Group 2. ANGULATS. 
ANGUIATE PCClINATR. se neverescecrencoes N. pectinata. N. pectinata, var. 
N. bivirgata. | cretee. 
ARGUNOTENCVIGOEE. — ss. 5 .onanconnacecanes N. gaultina. N. antiquata. 
L. Seeleyi. L. Vibrayeana. 
L. subrecurva. L. phaseolina.  L. lineata. 
Lupa. L. scapha. L. Marie. L. angulata. 
_L. spathulata. L. solea. 
Synonyms or species belonging to other families, to be definitely 
excluded are:—V. pulchra, Sby., and N. undulata, Sby. (Weera), 
NV. apwulata, Sby., N. subellipirca, Seeley, and N. rhomboidea, Seeley 
(synonyms). 
EXPLANATION OF PLATES III.-V. 
Puate IIT, * 
Figs. 1-3. IV. ovata, Mant. 
4,5. WN. capseformis, Mich. 
6-8. NV. albensis, d’Orb. 
9-11. WN. gaultina, Gardn. 
12-14, N. bivirgata, Sby. Fig. 14. var. ornatissima, D’Orb. 
* All the specimens on this Plate are in the author’s collection. 
