MUSEUM OK COMPARATIVE ZOOLOGY. 441 



The Anatomical Characters of Poromya (T. p. 280), Verticordia (I. 

 pp. 285, 2S(;), Cuspidaria (1. pp. 2!)3, liOiJ), Myonera (I. p. 3013), and re- 

 lated Forma. — In 188G I called attention to certain remarkable features in the 

 anatomy of the above mentioned form.s, anion*,' wliich were the facts that tlie 

 foot is set in a socket or chanil)er, like a stopper in a bottle, that in Cuspidaria 

 and Myonera gills in anythinj^ like the normal form of such organs are entirely 

 absent, while in Poromija and a group which I distinguished as Cdoconcha 

 there arc gill lamclhc of a very primitive type sparsely distributed on the 

 ventral surface of the septum which forms the floor of the upper half of 

 the peripedal chamber. In accordance with these investigations I modified the 

 classification of these animals, establishing three families for their reception. 

 Part of my material was in a rather poor condition, having been partially des- 

 iccated either before or after it had first been placed in alcohol, and that part, 

 especially in the Caspidariiclce, which was in good condition was represented 

 by very minute specimens. Since then, two years after the pul)lication of 

 my Report on the Pelecypods of the Blake Expedition, Dr. Paul Pelseneer of 

 Brussels has published in the Comptes Rendus of the Acadaniy of Sciences, 

 Paris,* and in a brief Report on the Anatomy of the Deep Sea Mollusca, in the 

 Challenger series, t some important observations on animals of the same groups. 

 To the facts brought forward by me, which were for the most part abundantly 

 confirmed, and the classification above referred to consequently adopted, he 

 was enabled, by the better character of his material, to add that the two halves 

 of the peripedal chamber correspond to the anal and branchial, or excurrent 

 and incurrent siphons, respectively; and that in the septum, beside the opening 

 in which the foot is set, there is a series of minute openings on each side of the 

 median line, which in Poromya are situated between the lamellae of the rudi- 

 mentary gills, and in Silenia Smith (non Mulsant, = Cetoconcha Dall) the 

 lamellae themselves have a subtubular form. lie also determined the existence, 

 in certain species of Cuspidaria, of minute rudimentary palpi, which the con- 

 dition of my specimens had not allowed me to observe, if present. In addition 

 to this he provided diagrammatic figures, which, if they cannot be said to illus- 

 trate w4th detailed anatomical accuracy the animals represented, at least enable 

 one to clearly understand what was present in his mind. We are therefore 

 under considerable obligations to Dr. Pelseneer, who has materially increased 

 our knowledge, and the fact that he has, as far as was possible, omitted refer- 

 ence to my prior observations and their publication in Part 1. of this Report, 

 does not render his confirmation of them less useful. 



However, in reviewing the subject with additional and well jDreserved mate- 

 rial collected by the U. S. Fish Commission Steamer Albatross in the AVest 

 Indies, and on her voyage thence to California, I am enabled to add to and 

 correct the data of the earlier part of this Report, and to advance the subject 

 beyond the point which it has hitherto reached. I hope also, that, in the con- 

 clusions which I draw from these observations, the relations of the forms in 



* Seance of April 3, 1888. 



t Vol. XXVII. Part LXXIV., 42 pp., 4 plates, 1888. 



