10 BRITISH MARINE TESTACEOUS MOLLUSCA : 
out the hopeless attempt of a rigid, natural, precessional and 
sequential progression. 
We almost think these facts and views go far to determine 
that the true progressive course of the essential order of 
nature of the class Mollusca, indeed of every other distinct 
class of animated nature, is within our reach, and that what 
we look for, depends on the more or less perfection of the 
reproductive system in each well-characterized group of the 
four grand types of the animal kingdom, in all which, if 
closely examined, we think the progressive advance of gene- 
rative organization is sufficiently apparent. 
ANALYSIS OF THE SYNOPSIS. 
First Division. 
ACEPHALA PALLIOBRANCHIATA. 
I have removed this section of the Acephala from its posi- 
tion at the head of the bivalves, to which I think it has no 
pretensions. I consider it a distinct inferior group forming 
the passage from the Ascidize and Cirripoda to the Acephala 
lamellibranchiata ; by its pallial branchiz it has relations with 
the Ascidize, and with the Cirripoda through the long convo- 
luted cilial buccal appendages, which, though not articulated, 
in consequence of advanced animality, still prove its connec- 
tion with that tribe. If the Palliobranchiata have the sexes 
distinct, as some authors have stated, the position I now place 
them in, with the strict hermaphrodite Acephala, would not 
be correct, and in harmony with my sexual distribution ; but 
I believe that these views of bisexuality in the bivalves are 
erroneous, and the causes that have led to them are those 
mentioned in the anatomy of Pholas dactylus under the head 
of the “‘ reproductive organs.” 
The Brachiopoda are very rare British productions: I have 
only met on the southern coasts with the minute Argiope 
cistellula ; but the Terebratula caput serpentis and the Crania 
anomala have been taken in North Britain sufficiently plen- 
tiful to determine their anatomical structure. I refer for an 
