32 Charles Zeleny. 



the branchial region and is large and massive. In some of the 

 species as P. triquetroides and V. multivaricosa it has a lateral 

 position and in others, as P. elaphus, a median one. 



These SIX groups form a very complete morphological series 

 which points strikingly toiuard the homology of the operciila and 

 hranchicB in all the forms. 



3. Distribution of the Opercula between Right and Left Sides. 



The data upon this point will be presented under this separate 

 heading because of their special interest in connection with later 

 discussions. The first three of the groups of Serpulids mentioned 

 above exhibit no asymmetry in their opercula and need not be 

 considered here. The three others will be discussed in turn: 



a. The fourth group have one functional and one rudimentary 

 operculum. Both opercular stalks have branchial pinnules. 

 (Examples — Apomatus, Josephella.) 



b. The fifth group have one functional and one rudimentary 

 operculum, each with a naked stalk. Rudimentary operculum 

 not on end of a long stalk. (Examples — Serpula, Crucigera, 

 Hydroides.) 



c. The sixth group have only one operculum. No rudimen- 

 tary operculum is present. (Examples — Ditrupa, Spirorbis, 

 Pileolaria, Pomatoceros, Vermilia.) 



(<3.) In the fourth group thirteen specimens of Apomatus were 

 examined and of these ten had the functional operculum on the 

 right side and the rudimentary on the left. The other three had 

 the reverse condition with the functional on the left and the rudi- 

 mentary on the right. 



Table II. 



Total No. 



F= Right F = Lert 

 R=Left R=Rieht 



Apomatus ampullifera 13 10 3 



Per cent • — 77 23 



(J).) In the fifth group Hydroides dianthus, H. uncinata, H. 

 pectinata and one specimen of Serpula vermicularis were exam- 



