SABELLIDES AND SERPULIDES 253 



completed before the valuable article 1 on Spirorbis, published by 

 Caullery and Mesnil in 1897, could be consulted. It was found that 

 these authors had made special and careful observations on the oper- 

 cula, with their calcareous plates, of many species, giving excellent 

 figures, as well as figures of the important collar setae. In connection 

 with their studies of material obtained at the laboratories of St.-Vaast- 

 la-Hougue on the English Channel, and from the French Expedition 

 to Cape Horn, these authors also borrowed specimens from the Museum 

 of Copenhagen (from Levinsen), the Paris Museum, and the Faculty of 

 Science of Lyons, besides special species from Marenzeller and Marion, 

 so that their list includes 27 species, 12 of which are described as new, 

 and their results far exceed in value any hitherto published. Owing to 

 the limited time allowed for the perusal of this paper, only the most 

 important facts could be noted, and it has been found impossible to de- 

 termine to what degree the following observations may be a repetition 

 of those of Caullery and Mesnil. 



In those species in which the embryos are developed in the tube, as 

 in S.spirorbis Linne 1 , S. spirillum Linne", S. asperatus sp. nov. etc., 

 the operculum is used simply as an organ of protection in closing the 

 aperture of the tube ; while in others, as S. granulatus Linn, S. 

 validus Verrill, S. stimpsoni Verrill, S. quadrangularis Stimpson. 

 etc., it has an added purpose, by being differentiated into a thin-walled, 

 pouch-like cavity in which the embryos are fully developed. It is 

 protected on the end by a calcareous plate or cap, varying in form, 

 having near its inner or ventral edge a more or less developed basal 

 portion. In species where there is but a slight basal thickening, as S. 

 semidentatus sp. nov., the plate appears to be more or less embedded 

 in the operculum, and minute protozoans, sponges, etc., are often 

 affixed to its exposed surface ; but in others, where there is an elon- 

 gated, more or less shield-shaped base, special muscles are joined to 

 the free end, apparently governing the movement of the plate, as they 

 appear to extend downward through the peduncle to the muscular 

 layer of the body, such muscle fibers often remaining attached when 

 the plate has been dissected. When the operculum becomes differen- 

 tiated into a brood-pouch a larger basal portion develops, which is 

 usually shallow behind and long in front, sometimes reaching nearly 

 the depth of the operculum, forming a stiff wall, thus protecting the 



1 Considerable difficulty was experienced in obtaining a copy of this article ; as 

 lack of time prevented application to the authors themselves, it was borrowed by 

 Mr. Van Name, the Librarian of the University Library, from the Surgeon 

 General's Office in Washington, D. C. 



