132 J. 8S. GARDNER ON BRITISH CRETACEOUS NUCULIDZ. 
Subdivision ANGULAT# PECTINATR. 
Gault Species. 
Nucuta prctinata, Sby. Plate III. figs. 15-16. 
Nucula pectinata, Sby., Mineral Conchology, vol. ii. p. 207. 
pl. 192, fig. 6-7 (1828). One of the types of the subgenus Port- 
landia of Morch. 
The dimensions tabulated are the extremes reached, and agree 
with those stated by D’Orbigny in the ‘ Paléontologie Francaise.’ 
The form does not vary to any great extent. The test is thick and 
strongly ribbed all over, except the lunule, and there are generally 
about 50 ribs on each side; the interior is nacreous and smooth, 
except the ventral margin, which is deeply denticulate. The spaces 
between the ribs, and sometimes the ribs themselves, are finely 
decussated by strice of growth, and there are always in adult speci- 
mens one or several furrows, or grooves parallel to the ventral 
margin. The teeth of the hinge are very strong and long, there 
being apparently as many as 24 on the longer one. It ranges with 
NV. ovata, except at Cambridge, where all the casts hitherto assigned 
to it belong to WV. biwirgata. The adductor muscles in the latter are 
situate much nearer to the umbo, and consequently further from 
the ventral margin, and are more salient; and the form of the cast 
is less produced posteriorly, more truncate and smaller. The species 
is widely distributed in France, over the Paris and Mediterranean 
areas. 
It does not occur either at Blackdown or at Speeton, as stated by 
various authors. 
NvcULA PECTINATA, Var. CRETH, var. nov. 
A pectinate form occurs in the Grey Chalk of Devon, which, 
while measuring only half the length of the Gault form, is consider- 
ably higher in proportion. The riblets are also perhaps rather 
finer, though it is difficult to judge of this in the condition in which 
the Grey Chalk fossils are preserved. It is obviously a distinct 
variety. 
Gault Species. 
Nucvzta prvireata, Sby. Plate III. figs. 12-14; Plate IV. figs. 
20-22. 
Nucula bivirgata, Sby. in Fitton’s “ Strata below the Chalk,” 
Geol. Trans. 2nd ser. vol. iv. p. 335, pl. xi. fig. 8 (1836). Including 
NV. ornatissima, D’Orb. Pal. Frang. vol. mi. p. 175, pl. 302, figs. 
9-12, 1843. Type of the subgenus Aca, H. & A. Adams. 
The dimensions tabulated are considerably exceeded in a few rare 
specimens, the largest I have measuring 25 mm. in length. The 
form is very variable, as shown by the fact that although D’Orbigny 
admits that the type, with zig-zag marking, may be a variety, the 
relative dimensions of his two supposed species differ very con- 
siderably. The test is thick, strongly ribbed all over, including the 
