K. J. Bush — Two genera of txibicolous Annelids. 55 



branous web. The peduncle arising from the outer base of 

 one of the lobes is compressed, with a thin gradually widening 

 membrane on each side terminating in a long tapered free end 

 at the base of the operculum, which, developing abruptly at 

 the back, is in profile somewhat triangular in form, deep in 

 front, oblique beneath, and truncated on top, capped by a 

 calcareous more or less flattened disk having an abruptly 

 developed asymmetrical cone-shaped mass or node of calcare- 

 ous deposit on top, often bearing a group of three conspicuous 

 spines, in other instances very irregular in outline ; none seen 

 forming a regular elongated cone as in Sowerby's figure 2c. 

 The thoracic membrane is conspicuously developed, forming 

 a deep rolling 3-lobed collar, the median lobe large, deepest in 

 the middle, with conspicuously fimbriated edge, the lateral 

 lobes less fimbriated, extending backward as a wide free lateral 

 border joining a deep angular posterior flap. Inside the collar 

 at the base of each lateral incision or cleft is an elongated 

 irregular-shaped organ. Collar fascicle small, the setae some- 

 what geniculate, with rapidly tapered blades ; other six fasci- 

 cles in very oblique series at the end of long tori situated in 

 the posterior border of separate membranous areas, the setse 

 simple tapered ; the uncini trapezoidal with 8 rather coarse 

 strongly curved pointed teeth, the terminal one square cut and 

 twisted. Abdominal setse a little flaring with serrate edge 

 and long slender tapered end. Yermilia triquetroides (Delle 

 Chiaje) is readily distinguished by the very different form of 

 the operculum and operculum cap, it being rather shallow, con- 

 cave beneath, but giving evidence of becoming inflated and 

 bulbous in form under favorable conditions; the cap is invari- 

 ably an asymmetrical calcareous cone roughened by concentric 

 lines of growth (see p. 52). 



There are 14 or 15 branchiae in each lobe united for a con- 

 siderable distance by a delicate membranous web. The tho- 

 racic membrane is much developed, forming a very deep roll- 

 ing 3-lobed collar, with conspicuously fimbriated edge merging 

 into a wide lateral border and deep tapered posterior lobe. A, 

 peculiar irregularly shaped elongated organ is attached inside 

 the collar at the base of each lateral cleft or incision. Philip pi 

 '44 and Lo Bianco '93 give the number of branchiae as 18 in 

 each lobe, so that the specimens under consideration cannot be 

 fully developed. 



Animals taken from" the tubes are beautifully banded with 

 blue. 



A very young specimen between 2 and 3 mm long, taken from 

 its tube, has the side appendages on the peduncle with the 

 very slender free ends at the base of the small angular opercu- 

 lum, which is capped by a simple unequally thickened calca- 



