30 Charles Zeleny. 



genera of any modification of the branchiae to compare with 

 the rudimentary operculum of Apomatus or Hydroides. The 

 right or left position of the operculum is definitely correlated with 

 the direction of curvature of the tube and as the latter is constant 

 for any one species the former must be also. In Spirorbis 

 Pagenstecheri the operculum serves as a brood pouch and is of a 

 trumpet shape. The branchial pinnules are comparatively large 

 and it is sometimes hard to tell whether a basal pinnule should or 

 should not represent a branchial stalk. <(Fig. 7.) Pileolaria sp. 

 also uses its operculum as a brood pouch. Other species, how- 

 ever (S. borealis, for example, according to Alex. Agassiz, '66), 

 keep the eggs in a string within the tube on the ventral side of the 

 body. 



Next comes the group in which the single operculum does not 

 occupy the line of the branchiae but is dorsal to it. First are the 

 cases in which it is lateral. In Pomatoceros triquetroides the 

 operculum is very large and stout. There are two lateral processes 

 beyond which comes an expansion ending in a cap of three spines. 

 There is a very pronounced suture near the base. The whole 

 region below the two lateral processes is flattened dorso-ventrally. 

 In the cases examined the operculum was always on the left side 

 (Fig- 8b, c). 



In Vermilia multivaricosa the operculum occupies a position 

 corresponding with that of P. triquetroides but it may be either 

 on the left or on the right side. The stalk of the operculum is 

 approximately circular in cross section though possessing a corru- 

 gated outer surface. It loops around from its point of attachment 

 toward the median line. The terminal region is thus brought 

 nearer to the median line than is the proximal region. The ter- 

 minal portion is very large and heavy. There is a basal globular 

 portion upon which rests a heavy cone-shaped body (Fig. 8d). 



Haswell ('85) describes a species of Pomatoceros (P. elaphus) 

 with a large median operculum which is short and flattened dorso- 

 ventrally. At the sides of the proximal portion are two wing-like 

 lobes bearing small processes. Terminally there are three pro- 

 cesses with antler-like branches. In another Serpulid (Vermilia 

 caespitosa), according to Haswell, there is also a large operculum 

 on a short stubby stalk (but not median judging by the figure, 

 though there is no statement in the paper on this point). This 

 operculum is armed terminally with peculiar spines and serrated 



