The chaetigerous lobes are small; the dorsal ones contain capillary chaetae, which are frequently confined to the anterior segments, whilst the ventral chaetae are uncini. The ventral surface of the anterior segments is thickened by glands which secrete the mucus employed in tube-building; the number of these "shields" and of the dorsal bundles of chaetae have to be noted in identifying the worms. There are one to three pairs of large anterior nephridia. A very strong "diaphragm"—usually more or less pouched—cuts off this anterior region of the body-cavity from the rest, and is the only complete septum in the body; from three to twelve pairs of small generative ducts occur behind it. The family is tubicolous, foreign materials being generally used in the formation of the tube. [Illustration: FIG. 175.—_Amphitrite johnstoni_ (½ nat. size). _g_, Gills; _t_, prostomial tentacles. (From Cunningham and Ramage.)] There are six genera which are fairly common round our coast, and their identification may be facilitated by means of the following table[388]:— {328} { equal in _Amphitrite_. { 3 pairs, { size. 24 notopodia. A. Capillary chaetae { which are { confined to the { { unequal in _Terebella_. anterior part of Gills { { size. 17 notopodia. body; commencing ramose. { on the fourth { { Gills equal. segment. { { Eye-spots. _Nicolea._ { 2 pairs. { { 17 notopodia. { Gills unequal { and of _Pista._ { peculiar shape. B. Capillary chaetae { arborescent; 3 pairs. _Leprea._ throughout the { body; commencing Gills { filiform; in transverse on the third { series in two _Thelepus._ segment. { segments. _Amphitrite johnstoni_ Mgrn. (Fig. 175) is brown in colour, about 4 to 6 inches in length, and nearly ½ inch in breadth anteriorly. Each of the gills consists of a curved stem; from the convex side of which arise a number of branches, themselves dichotomously divided, the final branches being long (Fig. 176, A). There are twelve ventral "gland shields." The worm is fairly common between tide-marks, below stones in muddy places: the end of its tube of mud projects above the surface. Atlantic.