Deep-water Limpets and Chitons. 13 
of the mantle and the foot (from a point above and behind 
the head) backward on the right side, attached only at its 
base. Anus anterior, opening above and behind the head. 
Mantle-margin plain ; sides and margin of the foot without 
papille or ornamental processes excepting two filaments, one 
on each side of the median line, between the mantle and the - 
foot-disk behind. Radula with a small or moderate rhachi- 
dian tooth (in the known species), three inconspicuous laterals 
with denticulate cusps, and a fourth, dentate, larger outer 
lateral* ; uncini numerous (50-150), similar, hooked at the 
tip, those of each lateral series springing from a common base. 
1 
This family differs from its nearest described allies (the 
Fissurellidee) in its single asymmetrical gill, in the absence of 
appendages to the sides of the foot or on the mantle-edge, 
and in its patelliform, unfissured, unsinuated, and wholly 
external shell. 
From the succeeding family, Addisoniide, it is separated by 
its symmetry, the character of the gills, and by its dentition. 
By its dentition it is most nearly allied to Parmophorus or 
Scutus (if figures be taken as a criterion), and much resembles 
some species of Helicina; but it must be borne in mind that 
very few species of Fissurellide have been figured in propor- 
tion to the whole number known. The other characters, how- 
ever, forbid its incorporation with the Fissurellide, as they 
conflict im nearly every important feature with the definition 
appropriate to that family. 
At first it was thought that Propilidium might be incorpo- 
rated in this family ; but an examination of the available data 
relative to that genus indicates that it belongs rather to the 
Fissurellidee, where it, apparently, represents an imperforate 
Puncturella. 
Formula: 
Genus Coccuttna, Dall. 
Animal blind; shell colourless, with radiating and con- 
centric sculpture. For other characters see diagnosis of family. 
Cocculina Rathbuni, n. sp. 
Shell depressed, white, thin, with sides nearly parallel, and 
their slopes lightly flattened, and with ends similarly broadly 
rounded; sculpture of faint closely (but irregularly) set 
grooves radiating from a smooth apex (which has originally 
a subspiral nucleus) and crossed by concentric growth-lines, 
* Much as in Scutus as figured by Gray, ‘Guide,’ p. 163, 
