52 J. S. Gardner—Cretaceous Gasteropoda. 
A. pes-pelecani section. Much as I should like to adopt a distinctive 
generic name for the Cretaceous group, I fail to find any characters 
by which to separate them from Aporrhais. 
Since I described the genus Dimorphosoma, the discovery of much 
more perfect specimens from the Grey Chalk at Dover has led me 
to remove one species, D. opeatochila, from that genus, and to place 
it, the only known British form, in the genus Helicaulax of Gabb. 
Dimorphosoma still remains by far the most distinct of all the genera, 
and embraces several American species. 
Helicaulax, Gabb (American Journal of Conchology, 1868, p. 143). 
Fusiform, anterior canal straight, more or less produced ; posterior 
canal long, ascending the spire to near the apex, usually deflected 
near the extremity; outer lip produced in a single falcate process ; 
inner lip usually heavily incrusted, the callus sometimes extending 
up the spire. The typical species is H. (Rostellaria) ornata, d’Orb. 
Helicaulax opeatochila, Gard., Grey Chalk, Dover. Pl. II]. Fig. 3. 
syn. Dimorphosoma opeatochila, Gard., Grou. Mac. 1875, p. 399. 
Shell small, length 23 mm.; spire elongated, angle 38°; whorls 
8 or 9, moderately convex; sutures distinct; markings, about ten 
rather obliquely inclined finely striated ribs on each whorl of the 
spire ; body-whorl with two angular and equal strongly tuberculated 
keels, below which are numerous tuberculated striz ; posterior canal 
same length as spire, attached to at least four whorls ; apex free and 
pointed; outer lip expanded laterally in a single process, ending in 
a long awl-shaped digit ; anterior canal short. 
The figure is restored from several specimens. The species 
strongly resembles H. ornata of D’Orbigny, but is smaller in size, 
and has more salient keels, and less pronounced tubercles (see also 
Grout. Mac. 1575, Dec. II. Vol. II. Pl. VII. Fig. 9; and Pl. XII. 
Figs. 23 and 24). 
It is found in the ‘cast bed” of the Grey Chalk near Dover, | 
where it is by no means common. Specimens are usually very 
indistinct and broken. 
Of the other American genera belonging to this family, I think 
we have a representative of Pterocella, Meek, in A. macrostoma, 
Sow., from Blackdown. There is, at all events, no other genus yet 
constituted in which this remarkable and unique fossil can be placed. 
Pierocellu, Meek. 
Shell small, thin; whorls few, rounded, smooth or subangulated ; 
last whorl not much enlarged; lip greatly extended and ascending 
the spire, trilobate, the middle lobe much larger and more produced 
than the others, carinated on the outer side. 
The above generic characters, with but slight modification, would 
embrace the Blackdown shell. 
The remaining Cretaceous genera, Phyllocheilus, Gabb, and Calyp- 
traphorus, Conrad, appear to be more Eocene in aspect, and have no 
representatives in the European Cretaceous rocks. 
