PLOTOBIA SIMPLEX. 155 



Plotobia simplex, sp. nov.^ 

 Plate 65, fig. 6-11; Plate 66, fig. 1. 



The body throughout is colorless and translucent. 



The total length of the type is 9 mm., with a maximum width of 2 mm. A 

 paratype from Sta. 4740 is 10 mm. long, and one from Sta. 4722 is 12 mm. long. 

 The number of somites is twenty-one. The body as a whole is somewhat 

 clavate in form, widening from a narrow caudal end forwards, but rounding in 

 toward the small head anteriorly. 



The prostomium is small in size and strictly conical in form, with the apex 

 dorsad. The tentacle seems to be partly lost in the type, in which it is repre- 

 sented only by a small, more transparent, spherical appendage at the tip of the 

 prostomium. The cirrus attached on each side at the base of the head is a broad, 

 suborbicular, foliaceous structure completely covering the prostomium in 

 lateral view. (Plate 66, fig. 1). 



The lower lip is thickened and bulges ventrad. From the inner edges of 

 the mouth there extends a semitransparent membrane continuous across the 

 ventral side and bending dorsad about the ends, so that its edges nearly meet 

 above, thus forming an incomplete funnel. 



The middorsal prominence attributed to the first free somite is rather 

 small, rounded, hemispherical. The branchiform process on each side arises 

 close to the base of the head; it is widest at the base, above which it narrows 

 strongly to the middle of the length and then but slightly distad to the rounded 

 tip; it is flattened dorsoventrally. (Plate 66, fig. 1). 



The single cirrus on each side of the first free somite is large, subquadrate, 

 attached broadly at one side. Each cirrus of the succeeding somite is larger 

 and more semicircular in outline. (Plate 66, fig. 1). 



The somites beginning with the third postcephalic one bear each two pairs 

 of well-separated cirri. Of these the notocirri increase caudad in size for 

 several somites and become more circular or sometimes subreniform in outline, 

 but with the distal end a little angularly extended. The neurocirri are smaller 

 than the notocirri. The first one is somewhat semicircular in general outline, 

 but presents a bulging rounded lobe dorsally and ventrally. The typical form 

 of neurocirrus as occurring farther caudad is ovate-acuminate with a broad base 

 which is lobed on each side, and so often appearing sagittate. (Plate 65, fig. 6-11). 



i^simplex,_^siinple. 



