240 CHITONID &. 
The Chitons have long been a source of difference of opi- 
nion with naturalists, not only as to their position amongst 
the Mollusca, but it has been insisted on, that they are apo- 
cryphal members of that class. The greatest authorities are 
in collision: M. De Blainville considers that the motive power 
and other apparatus of the circulation have a rectilinear dorsal 
arrangement, similar to that of the Annelida: Cuvier and 
Lamarck regard them as true Mollusca, ranging with the 
Patelloid group: Professor Forbes has doubts, and looks on 
the question as still within the limits of debateable ground, 
and terms the Chitons malacological “ puzzles.’ Some ob- 
servers contend, that the reproductive organs, unlike the 
asymmetrical ones of the Gasteropoda, exhibit a disposition 
of parities on a medial line, and lke M. De Blainville refer 
them to the Annelida. Milne-Edwards demurs that they are 
Mollusca, and goes no further than to regard them as an 
aberrant tribe of Gasteropoda. 
Having dissected many examples of three species, I think 
that my notes may assist zoologists im coming to sound con- 
clusions with respect to natural position. As my investiga- 
tions have induced a chain of reasoning which has convinced 
me that the Chitons are true Mollusca of the Patelloid type, 
it may be as well at once to allude to that part of them which 
bears upon the objections that have just been stated. 
Though doubts have lately sprung up as to the natural 
position of these curious animals, they have, until now, been 
placed by most authors in close connection with the Conchi- 
fera. If this is nght, what then is there extraordinary and 
unusual in the disposition of the organs of the circulation ? 
They have nearly the same dorsal rectilinear position as in the 
Acephala, from which they have long been considered, and I 
think it will be shown rightly, the point of transition to the 
Gasteropoda. Why not, therefore, contrast this peculiar 
arrangement, which is the invariable consequence of the sym- 
metry of the bivalve animal, with that which obtains in the 
Chitons from the same cause, and also in others of the Patel- 
loid tribe that have the same position and a similar parity 
of their organs? I admit, that the strict Patelle, though 
