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 terras. 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. Jeflfreys 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. S. Fish Commission steamer 



