1907.] NATURAL SCIENCES OF PlIILAUELrillA. 195 



DESCRIPTIONS OF NEW SPECIES OF SPIONIFORM ANNELIDS. 

 BY J. PERCY MOORE. 



Tlie following descriptions of four species of Spionidae and one of 

 i\Iagelonidae are based upon material mostly included in the collection 

 of Polychoeta belonging to this Academy, and which, with one excep- 

 tion, was secm-ed by the writer in the region about Wood's Hole, 

 Massachusetts. 

 Prionospio heterobranchia f^p. nov. 



This very interesting and distinct species is based iipon a single 

 imperfect specimen lacking the posterior end , and having a length for 

 the first 65 segments of 12 mm., and a maximum width at somite Ylll 

 of less than 4 mm. Form very slender, widest and depressed in the 

 branchial region, thence tapering very gently into the very slender and 

 suljterete posterior region. 



Prostomium (Plate XV, fig. 1) elongated cuneiform, tapering behintl 

 to a slender point which overlaps somite II and reaches to its posterior 

 margin; lateral margins with slight concavities opposite the ej'es for 

 the accommodation of the bases of the tentacular cirri; anterior margin 

 entire and broadly rounded; a conspicuous median ridge begins just 

 anterior to the eyes and, becoming more prominent, reaches to the 

 posterior end of the prostomium, where it forms a slightly free and 

 elevated process. Eyes one pair, very large and conspicuous, elongated, 

 black, situated close together at the sides of the median ridge and 

 between the bases of the tentacular cirri. No cephalic appendages. 

 Peristomium closely imited to prostomium, relatively small, some- 

 what pushed forward below as an oral papilla in the form of a truncated 

 cone; at the sides and above embracing the prostomium laterally as 

 slender, curved, lateral cephalic lobes much shorter than the prosto- 

 mium and ending in roinided enlargements anterior to the attachment 

 of the tentacular cirri, which have unfortunately been lost. Proboscis 

 protruded in the form of a short inverted cone with a somewhat crenu- 

 lated border extending slightly beyond the prostomium. 



Somites II to \T wider and much depressed ; \TI to X of the same 

 width but becoming deeper; after X the segments become gradually 

 more slender and terete and taper gently caudad. Branchial segments 

 very short, the others about § as long as wide and feebly marked. 



