474 THE ANNELIDA POLYCHAETA. 



h. Unoini subrectangular, usually not emarginate or but moderately so; free border thick, crossed 

 by numerous fine ridges at right '^angles to the margin; teeth exceedingly fine and appressed, 

 discernible only with difficulty, with at the anterior or lower end of the series a prolongation 

 or spine excavated below, gouge-like. 

 Setae of first somite replaced by a girdle of eyes; setae of the other thoracic somites limbate. 

 Operculum ending in a flat plate. Tubes crystalline. 



c. Abdominal setae weakly geniculate, limbate Placostegopsis St. Joseph. 



cc. Abdominal setae not of this form. 



d. Abdominal setae compressed cornuform, extended at one side into a long fine tap; thoracic 



membrane extending full length of thorax Placostegus Philippi. 



dd. Abdominal setae all fine, capillary, not limbate; thoracic membrane terminating with first 



somite Bonhourella Gravier. 



66. Uncini with free border not thus finely ridged, the margin bearing less numerous teeth that are 

 distinct and not compressed, 

 c. Uncini ordinarily tetragonal or trapeziform, with teeth comparatively numerous and fine, the 

 series terminating anteriorly, or below, in a large process or spine, which is nearly always dis- 

 tinctly excavated in gouge-like maimer. Abdominal setae compressed cornuform, with long 

 tip. 

 (/. Setae present on the first somite. 

 e. Dorsal setae of all thoracic somites alike, limbate, simply tapered. 

 /. Operculum preceded by two membranous wings and terminating in a flat or conical 

 plate bearing one or more (commonly tlu'ee) processes or spines. . . Pmnaloceros Philippi. 



}j. Operculum infundibuliform, bearing no spines Sjrirodiscus Fauvel. 



ee. Dorsal setae of the first somite of two distinct kinds; the setae of the other thoracic somites 

 limbate and simply tapering. 

 /. Operculum ending in a plate covered with a cluster of branching spines or bearing five 

 or six dichotomously divided laminae. 

 g. Operculum with a cluster of spines; special setae of first somite geniculate, with numer- 

 ous small spines at base of blade S/nrobranchus Blainville. 



gg. Operculum bearing five or six dichotomously divided plates; special setae of first 

 somite not geniculate, limbus broad, indented below tip, with no spines at base of 



blade Pomatoceropsis Gravier. 



//. Operculum bearing an axis to which are joined, often in the form of a pyramid, several 



separate plates Pomatostegus Schmarda. 



dd. No setae on the first thoracic somite. 



All thoracic setae simply limbate; operculum flat, with peduncle winged. 



Pomatoleios Pixel 1. 

 cc. Uncini with teeth fewer and less fine, the series terminating anteriorly in a tooth longer and 

 more obtuse than the others, tliis not excavated. 

 Abdominal setae geniculate, falcate, spiniform, or simply limbate, but never compressed 

 cornuform. 

 d. With special setae on the first somite. 

 e. Abdominal setae geniculate or falcate. 

 /. Tube small, calcareous, in a de.xtral or sinistral nautiloid spiral, or rarely in an ascending 

 spire. 

 Setigerous thoracic somites mostly three, sometimes three and a imlf or four, a long 

 naked region between thorax and setigerous part of abdomen; operculum with cal- 

 careous plate Spirorbinae, subfam. nov. 



g. Collar setae all or in part with posterior notch and fin. 

 h. All collar setae with notch and pronounced fin. 

 i. Tube sinistral. 



j. With four thoracic somites Protolaeospira Pixell. 



jj. With three and a half or four thoracic somites. 



k. Three and a half thoracic somites. . . .Paralaeospira CauUery and Mcsnil. 



kk. With three thoracic somites Spirorbis Daudin. 



I. Incubation in the tube subgen. ftpirorbis sens. str. 



II. Incubation in the operculum subgen. Pileolaria Claparfede. 



a. Tube dextral. 



j. With three and a half thoracic somites Spirorbidcs, gen. nov. 



jj. With three thoracic somites Spirorbella, gen. nov. 



