THE SESSILE BARNACLES. 3 



able to study a scries of Aiitillean deep-water forms, collected by the 

 United States Coast Survey steamer Blalce, and contained in the 

 Museum of Comparative Zoology. Tliis material has added con- 

 siderable to the account of American Veri-ucidae. 



Mr. John B. Henderson has furnished various deep-water species 

 dredged by his yacht Eolis. 



Several illustrations from the Bulletin of the Bureau of Fisheries 

 were lent by the Hon. George M. Bowers, late commissioner. 



Dr. W. H. Dall generously placed in my hands his fiiie examples of 

 Tamiosoma. 



Mr. Thomas H. Withers, of the British Museum, supplied photo- 

 graphs of the type of Lepas halanus Linnseus. Mr. C. Forster Cooper 

 kindly lent the type of Balanus xneas from the University Museum 

 of Zoology, Cambridge. 



Miss Mary J. Rathbun, Dr. Paul Bartsch, Dr. Thomas Barbour, and 

 others mentioned in the tQxt have furthered the work in various 

 ways. For all of these favors I wish to offer sincere thanks. 



Finally, I would express my appreciation of the faithful work 

 of Miss Helen Winchester, who made the drawings and retouched the 

 photographs of the work. 



TERMINOLOGY OF THE PLATES OF SESSILE BARNACLES. 



The armor of sessile barnacles is essentially similar to that of the 

 capitulum of pedunculate forms in being composed of calcareous 

 plates connected by chitinous intervals. Only the plates (scuta and 

 terga) bounding the cavity for the mouth, feet, etc., are movable, 

 the rest being so interlocked that they form a rigid wall, the plates of 

 which are termed comjMjiments. The chitinous band surrounding 

 the scuta and terga (or opercular valves) and connecting them with 

 the wall is called the operculai' memhrane. This membrane is moulted 

 like the exoskeleton of the limbs, and unlike other external hard 

 parts, which are permanent.^ 



The terminology of the plates is shown in figures 1 to 5. The 

 scuta, terga, carina, and rostrum are clearly homologous with those 

 of pedunculate barnacles. The lateral compartments are homologous 

 with part of the latera of the genus Mitella; probably they are 

 homologous with the three pairs of latera which are retained in the 

 genus Calantica. 



The exposed median triangle of each compartment is the paries 

 (pi. parietes). The edges of the compartments overlapping adjacent 

 compartments are called radii when they are differentiated from 

 the parietes by an alteration in the direction of the lines of growth. 

 The underlapping edges are called aide. The membrane or calcareous 

 plate upon which the barnacle stands is termed the basis. 



>.It should be noted that in some genera, such as Tubicindla, the upper layers of tho wall, and in various 

 Coronulinx the upper layers of the opercular valves are deciduous. 



