362 POMATOCERUS TRIQUETER. 
spines. Body wide in front, and with rather a broad tail. A median groove ventrally. 
Anterior region of six bristled segments; posterior of many segments. Anterior bristles 
capillary with tapered tips and narrow wings. Posterior bristles with slender shafts, which 
dilate into a broad shoulder with a curved and spinous edge and a terminal whip on one 
side. Anterior hooks triangular, with eight teeth above the probe-like modification of the 
main fang. Posterior hooks with seven teeth above the modified fang. Tube massive, 
white, keeled and fixed to rocks, stones and shells. It is looped and coiled in various 
ways. 
Philippi (1844) gave the following characters :—Operculum calcareous, hemispherical, 
with hollow appendages. | 
1. POMATOCERUS TRIQUETER, L., 1761. Plate CXVII, figs. 1 and 1b—body and tubes ; 
Plate CXXII, figs. 2 and 2a—branchia and operculum; Plate CXXXI, figs. 7—7d— 
bristles and hooks. 
Specific Characters.—The dorsal part of the collar forms a large, free lamella continuous 
with the broad ventral part, which is often reflected, and joins the alar membrane of the 
anterior region. It is dull yellow or brown externally at the branchiz, bluish internally. 
The branchize are somewhat short, and are grouped in two lateral fans of thirteen to eighteen 
filaments, which, tapering, end in a subulate process of some length. The pinne are short 
and taper slightly from base to apex. A pure white band runs round the base of the branchie, 
bordered by a band of red at each side. The base is madder-brown or violet. The filaments 
are barred alternately with white and red. The operculum springs from the dorsal edge of 
the left fan by a rounded stem, enlarges and flattens out as 1t goes upward and dilates into 
a flat cushion for the calcareous operculum, which is prettily marked with white, an ear-like 
process jutting out at its base on each side. Calcareous operculum may be conical, tubercu- 
lated, saucer-shaped, bifid or trifid. Body broad in front and with the alar membrane marking 
the first region, tapering to the rather broad tail; rounded dorsally, flattened ventrally on 
each side of the median groove ; six bristled segments in front, besides the collar-bristles ; 
many segments posteriorly. Dorsum anteriorly pale brown or purplish brown; ventral 
surface and posterior region dull yellow with pink laterally. Anterior bristles have straight 
shafts, with a slight bend near the tapering tip, which has narrow wings. Posterior bristles 
with slender shafts narrowed distally ; then dilated into a broad shoulder, with a curved, 
spinous edge and a terminal whip on one side. Anterior hooks triangular, with eight teeth 
above the probe-like modification of the main fang; posterior hooks with seven teeth above 
the modified fang. Tube massive, white, keeled, and with a sharp spine in front; fixed to 
rocks, stones, shells, ete. 
SYNONYMS. 
1727. Calcareous tube on shell of crab, Frankenau. Act. Acad. Caes. Leop., vol.1, p. 315, Taf. x, 
inex, IL. 
1747. Dentalium, Linneus. Westgotha Resa, p. 170 (paa Krabber). 
