58 PETTA PUSILLA. 



organs, held in the hollow between the two lobes which apply it to the free edge of the 

 tnbe — is accurately fitted, pours out the secretion that fixes it (Arnold Watson). 



Genus CXXXVIL— Petta, Malmgren, 1865. 



Cephalic area above the palmulae with an entire border; oral veil with a smooth 

 margin. Anterior border of the first segment emarginate in the centre ventrally and 

 crenulate, dentate at the sides. Row of eyes over brain. Nuchal organ folded as in 

 Lagis. Branchiae on the fourth and fifth segments (Nilsson). The ventral border of the 

 second segment with three notches in the centre, making two rounded lobes. Cement- 

 glands in fourth, fifth and sixth segments, opening between the second branchia and the 

 first bristle-tuft. Seventeen fascicles of bristles and fourteen lamellae for the hooks on 

 each side. Hooks, which commence on the third segment, pectinif orm ; two large teeth 

 in front, followed by a smaller, and a smoothly rounded prow. Bristle-like hooks of the 

 caudal process with straight shafts and slightly hooked tips. Anterior nephridia not 

 longer than the posterior. Tube very little curved, composed of minute fragments of 

 shells, coarse and translucent sand-grains, or minute flattened black and brown fragments 

 of rocks and shells. 



1. Petta pusilla, Malmgren, 1865. Plate CXXV, figs. 7— 7 g— bristles, hooks, scapha. 



Specific Characters. — Paleolae nine to eleven on each side, base pale with slight trumpet- 

 like enlargement, shaft flattened, a little dilated, and then tapered to a blunt rounded point. 

 Four to five of the exterior paleae stouter and broader than the others — Cams. Upper 

 area of the crown slopes obliquely backward and has no rim. It curves round the 

 ventral edge of the paleolae and ends at the anterior cirrus, a smooth area (of the crown) 

 occurring also below the paleolae, between them and the veil, which has a high arch and 

 a smooth border except at the highest point of the arch, where there are three papillae. 

 Ventral side of fourth segment has a plate with a knobbed lobe (Hessle). Body 

 15—24 mm. long, slightly tapered posteriorly so that the caudal appendix projects little 

 beyond its area. Dorsal surface smooth, flattened; dorsal rim of first segment nearly 

 straight, crenulate, or 5-dentate, and in the middle line a deep notch ; a rather long 

 row of hooks on either side, then a flattened lamella with a rounded posterior end and a 

 cirrus ; ventral rim follows with four fimbriae between this and the vent, the lower edge 

 of which is crenulate, with a subulate median cirrus. Eyes on scapha (fifth segment, 

 Hessle) ; eight to eleven anal hooks on each side. Nephridia in fourth, fifth, sixth, seventh 

 and eighth segments. A diaphragm occurs between the fourth and fifth segments. 



Bristled segments seventeen, divided into three anterior without hooks and fourteen 

 posterior with long rows of hooks. Bristles of two kinds— stout tapering bristles with 

 traces of wings distally, and those with a spear-head expansion of the tip which ends in 

 a hair-like point. Hooks on fourteen segments, with a short basal process or shaft, two 

 teeth below the crown, then a modified tooth with a spinous edge, and a smoothly rounded 

 prow beneath, the basal line from which is sinuous. Tube slightly tapered' and curved, 



