MOLLUSCOIDA. 
Crass BRACHIOPODA. 
The animals, and more especially the shells of this class of 
molluscoids, were for a long period regarded as belonging to 
true mollusca, and so uniformly are they still the objects of con- 
chological study that a treatise upon that science would be very 
incomplete for practical use, if the Brachiopoda were excluded. 
On the other hand, the two other classes of Molluscoida, the 
Tunicata and Bryozoa, are beyond the usual scope of concho- 
logical investigation, and as this work would be considerably 
increased in bulk and cost by the description and illustration of 
their systematic groups, they are omitted. 
Steenstrup, Morse, Kowalevsky and other eminent investi- 
gators, have concluded, mainly from embryological data, that 
the brachiopods form a portion of the subkingdom Annulosa, 
and are nearly related to the annelids or worms. Dall and 
Stoliczka have maintained the molluscoid affinities of the class. 
Thomas Davidson, who has made a specialty of the study of the 
Brachiopoda, summarizes the arguments of these naturalists and 
thus concludes : 
“No one can doubt that the brachiopods and Amphitrites 
possess many important characters in common after perusing the 
admirable observations upon the subject contained in Prof. 
Morse’s memoir; but at the same time, as was remarked to me 
by Prof. Verrill, almost any invertebrate group may be annelid- 
elized by overrating certain points of its affinities; and it 
seems to me that one must not place entire confidence in any 
classification which is founded to so great an extent on embryo- 
logical characters.” 
Huxley writes: ‘“ The acceptance of the view originally pro- 
pounded by Steenstrup and so ably urged by Professor Morse, 
respecting the affinities of the brachiopods with the worms, does 
not to my mind weaken the opinion I have always held as to 
their affinities with the Bryozoa on the one hand, and with the 
higher Mollusca on the other.” 
