64. 



OQITOIIQLiQaY . 



21. Verrill and Bush. Revie-vr of the Genera of the 

 Ledidae an.d Nuculidae of the Atlantic Coast of tlie United States. 

 Am, Jour, of Sci. Vol. 3, 1897. 



22. "ITilson E. B. Origin of the Me sob last -Bands in 

 Annelids, Jour, of Morph. Vol. 4, 1890. 



KEY TO LETTERS. 

 aa. Anterior adductor muscle. 



ac. Apical cilia. 



ae. Anterior projection of the mantle margin, 

 afm. Anterior foot muscle, 



ap. Apical plate. 



bg« Bji-ssal gland. 



bl. Blastopore, 



bs. Blood space, 



eg. Cerebral ganglia, 



cr. Chit^nous rods, 

 cvc . Cerebro -visceral commissure, 



ec. EctodeTTn. 



ep . Ep i t ho 1 ium . 



es, Exhalent siphon, 



f . Foot . 



