PARATHELEPUS. 183 



a longer and a shorter, the latter alternating with the former. The longer bristles (Plate 

 CXXVI, fig. 7) have nearly cylindrical shafts inserted deeply in the tissues, but they 

 taper from the cuticular surface distally so that when the narrow wings commence 

 considerable diminution has occurred, and they taper to very fine hair-like curved points. 

 The shorter forms are much more slender, but they also taper to hair-like points and 

 have narrow wings. The dorsal edge of each fascicle is bounded by three or four strong 

 bristles without the intervening shorter and more slender forms, whereas the ventral edge 

 has shorter and more slender bristles. 



The number of bristle-tufts is about thirty-two, and the region behind has only 

 uncinigerous lamellae. The posterior bristles are also inserted deeply in the tissues, are 

 stout and comparatively short and have considerably broader wings, but they likewise 

 taper to a fine hair-like point. They retain the same arrangement of the three or four 

 strong bristles without the intervening slender forms on the dorsal edge of the tuft. As 

 the shorter, slender forms do not present traces of wings it is doubtful if they represent 

 reserve-bristles. 



The first row of hooks commences opposite the fourth bristle-tuft, that is, in a 

 corresponding position to that of T. triserialls, though in the latter it is the third 

 setigerous process. The rows are somewhat shorter than in Thelepus, and they are sooner 

 elevated on ridges ; indeed, at the eighth or ninth a distinct lamella is apparent, and at 

 the twenty- fifth it forms a fan-shaped flap with the single row of hooks in a curved line 

 on the anterior face of the edge. The hooks of the first are distinguished by the apparent 

 length of the base, but this is due to its narrowness. The typical hook (Plate CXXVI, 

 fig. 7 a) has two distinct teeth above the main fang, the crown above it being thus 

 elevated; the posterior outline is deeply indented, the anterior outline (below the main 

 fang) has a peculiar stud which leaves it at an obtuse angle, whilst the prow is continued 

 beyond it to end in a process for a ligament ; the base is evenly convex inf eriorly, and has 

 a process at the end of the posterior outline. 



The tube is soft, rather thick, and composed of grey, muddy sand in fine grains. In 

 that dredged by the " Porcupine " the soft, translucent, yet fairly tough secretion had 

 minute grains of sand attached to it at intervals. Thus the tube is readily distinguished 

 as a rule from that of Thelepus cineinnatus. 



Sars 1 (1871), in the characters of the genus, gave the hooks only two teeth, but in the 

 British examples there are three. 



Ehlers 2 (1875) describes from the " Porcupine " Expedition a species termed Grymxa 

 brachiata, n.s., but the figures, for instance, of the hook are so indefinite that some doubt 

 remains as to its exact nature, for the slight differences noted by the author, such as the 

 occurrence of the hooks on the sixth segment, may yet be otherwise explained. 



Genus CLIV. — Parathelkpus, Gaullery, 1915. 



Cephalic region with a frilled lobe around the mouth, the sides separated ventrally 

 and partially dorsally ; an independent small lamella behind the mouth. Tentacles 



1 < Vidensk-Selsk. Forhandl. Christ./ p. 10. 



2 'Zeitsch. wiss. Zool./ Bd. xxv, p. 74, Taf. iv, figs. 24—27. 



