50 J. S. Gardner—Cretaceous Gasteropoda. 
described as Helicaulax bicarinata and H. costata, a new genus of 
his own, in which they appear to be incorrectly placed. It would be 
possible either to retain the genus Ornithopus by limiting Tessarolax 
of Gabb strictly to the incrusted and tuberculated forms, which 
would practically make it obsolete ; or to make the latter embrace 
Ornithopus by omitting the tuberculation and incrustation of the 
whole spire as generic characters. 
Upon consideration, I think the simpler way, and the one most 
likely to be accepted unanimously by paleontologists, is to abandon 
Ornithopus and adopt Tessarolaw in the wider sense, two separate 
genera being clearly unnecessary. I therefore adopt Tessarolaa, 
according to Gabb’s second definition, omitting as generic characters 
the presence of tubercles and complete incrustation of the spire, 
which are only rarely and abnormally present. 
Tessarolax, Gabb. (American Journal of Conchology, 1868.) 
Shell subfusiform, spire and aperture about equal ; part of, or the 
entire spire and body-whotrl incrusted by an extension of the inner 
lip of the adult; anterior canal long, curved or straight ; posterior 
canal long, running up the spire, and extending considerably beyond 
it; outer lip expanded, generally carrying two long, slender, digitate 
processes. Whorls 5 to 6, always striated and bicarinated, without 
transverse ribs. Angle 374° to 40°. The incrustation of the adult 
shell very exceptionally forms tubercles on the body-whorl. 
This genus, to a slight extent, links the Strombide and Aporrhaide 
together, but its affinities are with the latter. 
Tessarolax, sp. nov. PI. III. Fig. 2. 
This fragment possesses all the characters of Tessarolaz, and is 
similar in type to T. retusa, the small extent of the region of the 
body-whorl in front of the keels giving the shell a truncated, in- 
stead of a pear shape. The species was evidently finely striated, 
and the keels appear to have been slightly tuberculated, as in 
T. Fittoni. It was a larger shell than either of the Gault or Neoco- 
mian forms; but less than the Grey Chalk T. oligochila. It is 
scarcely sufficiently perfect to furnish specific characters. The 
unique specimen figured belongs to Mr. J. F. Walker, and is from 
‘Upware. 
I have also figured (Fig. 1) a more perfect example of T. oligochila, 
Gard., from the Grey Chalk. This species proves to have possessed 
a more expanded wing than I was led to expect from the specimen 
first found, but it is never cut up into separate digits, as in most other 
species. 
The genus Zridactylus remains unchanged, and has so far stood 
the test of time. Another species, sent to me by Mr. Walker, has to 
be added. 
Tridactylus Walkeri, Gardner. PI. III. Fig. 4. 
Shell elongate and pupeform; whorls irregular, inflated, not 
forming a regular cone; possessing a strong central keel, a second 
and less prominent keel in front, and two partly concealed sutural — 
keels. The body-whorl has two nearly equal keels (slightly diverg- 
