ANATOMY AND DLASSIFIOATION OP THE AHENICOLID/E. 541 



entire. Gonad small. Found on both sides of the North 

 Atlantic and on the western coasts of America. 



(a) A. marina. Thirteen pairs of gills (the first may be 

 reduced)^ dendriform or pinnate. Otocysts opening to the 

 exterior. Otoliths many, composed of foreign bodies (quartz 

 grains, etc.). Sis pairs of nephridia opening on segments 

 4 — 9. One pair of oesophageal pouches, cyliudrical^ club- 

 shaped, or conical. Diaphragmatic pouches (on the first 

 diaphragm) small, globular, or flask-shaped. Ova spherical, 

 with thin vitelline membrane. 



(b) A. Claparedii. Lateral lobes of prostomium well 

 developed. Thirteen pairs of gills, pinnate. No otocysts. 

 Five pairs of nephridia opening on segments 5 — 9. Two or 

 more pairs of oesophageal pouches, papilliform, digitiforra, or 

 filiform. No diaphragmatic pouches. Ova spherical, with 

 thin vitelline membrane. 



(c) A. cristata. Eleven pairs of gills, pinnate. Otocysts 

 closed, spherical sacs, each containing a single large spherical 

 chitinoid otolith. Six pairs of nephridia opening on segments 

 6 — 10. CEsophageal pouches as in A. marina. Diaphrag- 

 matic pouches large and finger-shaped. Ova spherical, with 

 moderately thick vitelline membrane. 



II. No tail, the parapodia and gills continued to the pos- 

 terior end of the animal. Body generally of uniform diameter. 

 Number of gills variable, gills branched unilaterally. Pro- 

 stomium simple, conical, non-lobate. Brain commissural. 

 Otocysts closed spherical sacs, otoliths spherical. Diaphrag- 

 matic pouches long and finger-shaped. Oesophageal pouches 

 flask-shaped. Nephridia with dorsal lip bearing somewhat 

 cylindrical, digitiform, often branched, ciliated vascular pro- 

 cesses ; ventral lip deeply notched in the middle, the two 

 halves semicircular in shape. Ova generally oval, with thick 

 vitelline membrane. 



(a) A. Grubii. First gill on segment 12 (may be small), 

 five pairs of nephridia opening on segments 5 — 9. Gonad 

 small. Twelve to twenty-eight pairs of gills. 



(&) A. ecaudata. First gill on segment 16. Thirteen pairs 



