174 BULLETIN OF THE 
lar wrinkles to compound and very complex lamellar organs. If ordinal 
distinctions exist in the Pelecypods their fundamental basis has yet to 
be made clear. 
The present paper is prefaced with some general observations on 
abyssal mollusks, the essential principles of which have appeared in 
several scattered articles, at various dates, but which I have thought 
it would be well to bring together and elaborate a little on the present 
occasion. I have added a systematic table of the species referred to 
in this part of my Report, deferring a complete and alphabetical index 
until the whole shall be printed. 
I have included the Brachiopods under the general title of Mollusca, 
because I believe that, on the whole, the characters they present are 
those of animals most nearly allied to Polyzoa and Mollusca, and that 
there is nothing to be gained by splitting up the sub-kingdom thus con- 
stituted, however clearly we may recognize its subdivisions. The dis- 
memberment which has been proposed by various authors is more a 
matter of phrase than of biological distinction. The intimate relation 
of the Mollusks, as a group, to the Worms, is indicated by many embryo- 
logical and histological characteristics. The indebtedness of all the in- 
vertebrates to the vermian stock would bankrupt them to pay. To say 
that the Brachiopods are Worms, in any proper or literal sense of the 
words, appears to me as absurd as it would to assert that Vertebrates 
are Ascidians. It is a clear case of including the greater in the less. 
The relations are there, and should be fully recognized ; but the subject 
should not be clouded by the miscomprehension of systematic values, 
or the misuse of systematic terms. It should not be forgotten that our 
knowledge of the development and even the adult anatomy of the 
Mollusca is trifling compared with the field which remains unexplored. 
Until more is known, we can well afford to acknowledge the inadequacy 
of the basis for any comprehensive statement of relations which may be 
termed conclusive. 
During the progress of my studies I have had the privilege of con- 
tinuous and friendly consultation with two veteran naturalists, Dr. 
Thomas Davidson and Dr. John Gwyn Jeffreys, who now rest from 
their labors. In the latter case, I have also had the advantage of be- 
ing able to consult the original collection of Dr. Jeffreys now forming 
part of the U. S. National Museum. 
To Prof. Spencer F. Baird, Director, and Mr. G. Brown Goode, Assistant 
Director of the National Museum, I am indebted for the opportunity for 
study of the collections made by the U. 8. Fish Commission steamer 
