^°i'89^"] PROCEEDINGS OF THE NATIONAL MUSEUM. 291 



a surprisiii;,^ iiiunber of cases, consideriiij; the apparent difliciilty of 

 accomitiii^' for their preseuce, in i)airs also, iuside tubes they cau uot 

 escape from. 



Thus in ten tubes examined were found tliree pairs of PorceHaua 

 and four pairs of Pinnixa, besides a small Pinnixa and two very small 

 crabs. In all cases cue male and one female inhabit a 8inp:le tube, 

 thon^^h perhaps one tube was found with only a sinfjle male. The 

 breeding' season of Cha'toi)terns seems to extend over the entire sum- 

 mer; even on Sei)tember 20 eg:gs were discharj,^ed from the dorsally 

 l)laced nephridial openings of a female kept in the aquarium. This 

 discharge of eggs may often be readily brought about by adding a fresh 

 sui)ply of sea water to rei)lace that the animal lives in. Perhaps there 

 is a tendency to discharge eggs at the time of rising tide. 



Family SPIONIIU:. 



NERINE Joliiistoii. 

 Nerine agilis Vt-rrill. 

 Verkill. Invert. An. Vineyard Sil., p. 34(>, (ioo. 



Very abundant in the sand on the outer beaches and at Fort Macon, 

 perforating it with very numerous slender vertical holes. Often washed 

 out by the waves they ipiickly burrow again into the sand, if not cap- 

 tured by birds. 



POLYDORA Bosc. 



Polydoia caeca Webster. 



Annel. Clia>t. Virginian Coast, p. frj, PI. i.\, Ki^'s. llH-ll'-i. 

 This Annelid is quite common, perforating dead shells. 



Polydora commensalis. sp. nov. 

 (Plate XIV, Fig. 27.) 



Body flat ventrally, somewhat convex dorsally, flattened posteriorly 

 and rapidly tapering. Tentacular cirri in contracted state equaling 

 diameter of body, flattened, with ciliated ventral groove. Cephalic lobe 

 small, siini)le, rounded in front; lateral lobes rounded ; eyes black, pos- 

 terior pair smaller and nearer together. Both ce|)haliclobe and buccal 

 somite usually retracted within lirst setigerous segment in preserved 

 si)ecimens. First four setigerous .somites bear a dorsal and a ventral 

 cylindrical cirrus or i)apilla shorter than diameter of tentacular cirrus, 

 and with a fascicle of .<ilender seta' at the base of each. Fifth somite, 

 with a decreasing series of six stoat, amber-colored seta' bent at tips, 

 and with a thin lamelliform ex|)ansion on the concave side. Close to 

 the base of these arises a small fascicle of short, delicate .seta', similar 

 to those of the prectMling somites. 



Kranchia' begin ui)on tiie sixth setigerous somite, rapidly increase in 

 length, equal half the diameter of the body and persist throughout, 



