MOLLUSCA., 789 
Sexes distinct. Tongue long, linear, mostly beset densely with 
teeth and barbs. Shell resembling a shield, dorsal, not turbinated, 
with aperture ample. 
The position of the branchiz brings this family into the neigh- 
bourhood of the Hypobranchiata, and thus Lamarck refers Patella 
and Chiton with Phyllidia to the same family. In other respects, 
however, there exists much difference amongst these animals, as at 
once appears from the disposition of the sexual organs, since in 
this division the sexes are distinct. Still, in a natural sequence of 
the animal kingdom, the Cyclobranchiata ought to form as it were 
the transition of the Ctenobranchiata to the three preceding families, 
the Opisthobranchiata of Minne Epwarps. 
That some individuals of Patella are female, others male, was observed 
by Gray (Annals of Nat. Hist. 1. p. 482), by Minne Epwarps (Annales 
des Sc. nat., 2e Série, X11. p. 376), by Purers and Rosin (MUELLER’S 
Archiv, 1846, s. 134) and by WAGNER (besides in Patella) also in Chiton 
(Annals of Nat. Hist. vi. p. 70). 
Chiton L. Shell multivalve, made up of (eight) testaceous 
scales arranged in a longitudinal row, incumbent on back. Mantle 
at the circumference not covered by shell, with margins hard, 
coriaceous, often aculeate or squamose. Ventral disc elongate, 
narrower than body. Eyes and tentacles none; head crested by 
a wavy veil. 
With Liyyzvs there are three genera of Jestacea multivalvia : 
Chiton, Lepas and Pholas. The last genus belongs to the Conchifera 
or biwalvia ; Lepas is, as we stated above, a family of the Crustacea. 
Thus there remains the genus Chiton alone as a true multivalve 
mollusc. That it has no affinity or true similarity with the Cirri- 
pedia (Lepas L.), to which BuatnvitLe united it under the name of 
Malacoéntoma, now requires no demonstration ; but many authors, 
both of earlier and later periods, still maintain that it differs too 
remarkably from the rest of the Gasteropods to allow it to remain 
in the neighbourhood of Patella, and that it forms the transition to 
the ringed worms (Mi~nE Epwarps Ann. des Sc. nat., 3e Série, rx. 
1848, p. 110). It appears to us that these writers attach too much 
weight to the external resemblance of the pieces of shell to rings of 
articulate animals. In the internal structure there is, perhaps, with 
the exception of the remarkable occurrence of two oviducts (or vasa 
deferentia), and two sexual apertures placed at the side, nothing to 
be met with that can indicate a remote affinity with the Articulata. 
