NAINEREIS RETUSICEPS. 355 



Nainereis Me'^nil and Cat'llery, Hull, sciontif. 1898, 31, p. 143. 

 Nainereis McIntosh, British annelids, 1910, 2, pt. 2, p. 516. 

 Theodisca F. Mulleu, Archiv. naturg., 1857, 24, p. 1. 



Nainereis retusiceps, sp. nov.^ 

 Plate 65, fig. 3-5. 



The general color is yellow, of a slightly brownish cast. 



The body is moderately long and slender, depressed, but little, convex 

 above and decidedly more strongly arched below, not grooved. At the caudal 

 end the body is flattened, thin and wedge-shaped. It is also somewhat similarly 

 flattened at the anterior end (inclusive of peristomium) . The body is narrow 

 in the region just in front of the middle, from where it -widens distinctly both 

 cephalad and caudad. The total length of the type is about 18 mm. and the 

 width in the anterior broad region is 1.9 mm., exclusive of the parapodia, and in 

 the broadest region caudad of the middle, about 2 mm. There are about one 

 hundred and sixty-five very short and closely crowded somites. 



The prostomium is wide and rather short, anteriorly bluntly rounded. It 

 is flattened dorsoventrally, deepest at base. There is a shallow median longi- 

 tudinal sulcus above. At the middle of the length there is a shallow transverse 

 furrow which on the sides is deeper, forming conspicuous notches, in each of 

 which the nuchal organ lies. The median longitudinal furrow extends around 

 the anterior end and continues caudad beneath as a wider furrow extending 

 to the mouth. 



There are no eyes or appendages. 



The peristomial region is double, the two rings, wholly achaetous and 

 without appendages, are less strongly separated above but are very distinct 

 laterally and ventrally. Together they narrow cephalad like the frustrum of 

 a cone. The two together are above shorter than the prostomium and longer 

 than the first setigerous somite, though decidedly less than twice so. On the 

 ventral side the anterior ring is incomplete, each end lying at the lateral border 

 of the mouth, and lying partly in an excavation of the posterior ring, which ex- 

 tends forward between the ends of the anterior one to limit the mouth on its 

 caudal side. This median region of the second ring, the labium, is straight 

 anteriorly and is crossed longitudinally by fine sulci, which at the sides are 

 somewhat oblique. 



The metastomial somites are all extremely short, in the widest anterior 



1 retusus, blunt, ceps, head. 



