388 CRETACEOUS GASTROPODA 
very slender, the eyes are placed on thickened, prominent bulgings at their 
outer base; head lobes are always present, either single or bilobed; the mantle is 
fissured in front. -'The dentition in general resembles that of the ScuTrBrancHiAta, 
being characterized by a very large number of equally formed, slender, outer laterals ; 
of the inner laterals there generally are on either side five, being much larger 
than the outer ones; those next to the small central tooth are beamlike, deeply 
notched on the inside edge, the other four are broadly hooked and pointed. The 
branchial cavity lies, according to the observations of Cuvier, on the left side of 
the central adductor muscle; there are two long subequal plumes present. 
The shell is ear-shaped, consisting of few, very rapidly increasing, depressed 
whorls, spire very short, usually flattened ; along the inner or left edge of the whorls 
are placed a number of separated holes, some of which near to the apertural margin 
are always open for the purpose of supplying water to the branchial cavity, this 
being apparently accomplished by the vibration of some of the left upper filaments of 
the fringe projecting through the openings. The aperture is very large, internally 
pearly, with the inner lip obtuse and more or less flattened. 
H. and A. Adams (Gen. I, pp. 440-443) distinguish in this family three genera 
and one subgenus. Comparing, however, both shells and animals, it must be 
eranted that the distinctions pointed out as existing between the various types 
are only of minor importance. 
1. Haliotis, Linn., 1740, has a roundish or ovate shell, being depressed or 
slightly convex, usually spirally striated and often transversally laminated. The 
animal usually has a moderately expanded foot. The European H. ¢uberculata, L., 
may be considered as the type of the genus, 
1a. Teinotis, H. and A. Adams, 1854, has a very oblong shell, but otherwise 
not different from that of Haliotis. The foot of the animal is very largely, 
posteriorly produced and provided with a deep, superior longitudinal groove. The 
type is HZ. asinina, Linné. 
4 b. Padollus, Montf., 1810, is distinguished from Haliotis by the presence 
of a spiral ridge between the suture and the row of perforations. Some species 
of this section of Haliotis have the ridge quite close to the row of perforations; 
for these the subgenerie name Szlewlus has been proposed by H. and A. Adams. 
Until it can be proved by farther researches that none of the animals of the 
species, at present referred to Haliotis, have above a posterior groove, the distinction 
of Teinotis must be considered only as of subgeneric value, for the form of the shell 
is, for instance, scarcely much more oval than that of H. lamellosa, Lam. Again, 
comparing some of the transversally ribbed species, like H. Kamtschatkana, Jonas, 
with typical Padollus, it will be seen that the line of distinction is extremely diffi- 
cult, and in some cases almost impossible to draw. ‘The transverse ribs terminate 
some distance from the suture about the middle of the last whorl, and form here 
strong tuberculations which, if united, produce the spiral, continuous rib. Other 
species of Haliotis, like H. papulata, Reeve, show several stronger ridges, but neither 
these, nor the transverse ones, are constant. 
