VIII. PlIYLOGENY OF THE PeLKCYPODA. 

 The AvicuLiDiE and their allies. 



By Robert Tracy Jacksojt, S.D. 



contents. 



I. Introduction . . . . p. 277 IX. Pecten : anatomj' and liahits . p. 333 



II. Sources of material and niotliods of X. Pecten : the shell . . . p. 342 



work ..... p. 284 XI. Genera allied to Pecten . . p. 350 



III. Classification of stages of growth and XII. Anomia : anatomy and habits . p. 3,54 



decline p. 288 XIII. Anomia : tlie shell ... p. 359 



IV. Ostrea: development of the. «oft parts; XIV. Studies of a few other genera . p. 362 



embryology .... p. 294 XV. On the genetic relations of the Pro- 



V. Ostrea: development of the soft parts ; dissoconch .... p. 375 



the spat ..... p. 303 XVI. Genealogical connection of tlie 



VI. Ostrea: development of the shell p. 311 Aviculid* and their allies . p. 379 



VII. Gryplitea, Exogyra and adult Ostrea, XVII. List of papers quoted or referred 



with a consideration of the mechani- to in the text ... p. 394 



cal origin of the ostrean form of shell p. 317 XVIII. Description of plates. . . p. 395 

 VIII. Perna, Avicula and near allies . p. 327 



I. Introduction^. 



iyXy pala^ontological studies have been can-ied on at the Museum of Comparative Zo- 

 ology as a pupil and assistant, fii'st of Professor Xathaniel S. Shaler and later of Pro- 

 fessor Alpheus Hyatt. To these gentlemen first are due my acknowledgments in this 

 paper, which was offered as a th'esis for the degree of Doctor of Science at Harvard Uni- 

 versity May 1, 1889.^ Aclvnowledgments are next due to Mr. Alexander Agassiz for 

 the opportunity to study the collections in the Museum. 



The investigations on which this paper is based were made while associated with Pro- 

 fessor Hyatt in the Palseontological Department of the Museum.^ I have applied some 

 of the principles which he has deduced as a result of his scientific work, but I wish to 

 state that he has never urged his views u]ion me, or pointed out their application in the 

 Pelecypods. At Professor Hyatt's special request, I have used entire freedom in reject- 

 ing or criticising his views whenever they seemed not in accordance with the facts pre- 

 sented. 



' On account of new material oljtainuti, some adcli- liave been made to sections viil and xiv, and are uidl- 



tions have been made to this paper since it was read be- Gated Ijy the date of tlie collecting of the material, 



fore the Socitty on April 3, and since it was offered as 'Three years have been spent in that department as- 



a thesis on May 1, 1889. The additions for the most part sisting Professor Hyatt aiianging the great collections of 



MEMOIRS BOSTON SOC. NAT. HIST., VOL. IV. 



Fossil Invertebrates. 



(277) 



