APOMATUS AMPULLIFERUS. 375 
tube is more transparent than in the ordinary P. tridentatus, and the spines especially so. 
It represents, however, only a variety of P. tridentatus, J. C. Fabricius. 
Genus CLXXXII.—APomMaTUs. 
Cephalic collar narrower, but thicker than in Placostegus. It fuses with the alar 
membrane and passes ventrally as a continuous fold. Branchiz rather soft and thick, of 
moderate leneth; often coiled and doubled; seven filaments on each side, with short 
terminal processes, one on the right bearing at its blunt extremity-a short pedicle for the 
soft globular operculum. Anterior region of seven bristled segments, with a broad alar 
membrane. Ventral surface marked by a median groove from end to end. Anterior bristles 
have finely tapered tips and distinct wings. Posterior bristles confined to the caudal 
region, and they have short shafts, and broad, sickle-shaped, serrated and striated terminal 
blades. Anterior hooks avicular, with a rounded crown, a long and minutely serrated 
anterior edge, with a modified fang inferiorly, a gulf beneath it, and a rounded prow. 
Posterior outline indented. Tube more or less curved or coiled, a rounded aperture, with 
a flat ridge between two slight grooves running dorsally from end to end. 
Philippi (1844), who constituted the genus, gave it no operculum, the other character 
being the continuation of the lateral (alar) membrane half the length of the body, and equally 
broad. He, indeed, was in doubt about the species Apomatus ampulliferus, having only 
seen a single specimen, which he would have regarded as an abnormality if Scacchi had 
not observed the fresh animal. 
De St. Joseph (1894) observes that this genus is transitional between Protula and Filo- 
grana. Like Protula, it has feeble branchial filaments, ordinary winged bristles on the first 
segment, hooks with a long terminal process not hollowed beneath, a long white dorsal keel 
(caréne) to the end of the body. But it approaches Filograna in size, by its operculum at 
the tips of one or two branchie, which conserve their barbules, and by the naked anterior 
region of the abdomen. The abdominal bristles (“en faucille”) are like those of Protula; 
they are geniculated and serrated as in Filograna (A. ampulliferus). Yet it belongs to neither 
Filograna nor Protula—since he had not found the thoracic brush-like bristles (en faucille) 
in either. He thought the globular operculum a secondary character. Marenzeller again 
separates the genera Apomatus and Protula for other reasons, namely, the appearance of the 
hooks on the second segment in Apomatus, whereas in Protula they appear in the third 
segment, and the thoracic and abdominal bristles approach each other in structure. De 
St. Joseph, however, found hooks on the second segment in Protula tubularia, and so did Sars 
in P. borealis. He concludes by observing that Protula has not the thoracic bristles of 
Apomatus and no operculum. 
1. APOMATUS AMPULLIFERUS, Phalippz, 1844, Plate CXXXII, figs. 2—2c—hristles, oper- 
culum and branchia ; Plate CXX XVII, fig. 19—hook. 
Specific Characters.—Collar less developed than in Placostegus, but, though narrower, it 
is thicker and follows a similar arrangement, as, starting from the dorsal edge of the fused 
