PLACOSTEGUS TRIDENTATUS. 371 
a flattened tail, rounded dorsally, flattened and grooved ventrally. Anterior region with 
six bristled segments, the bristles being simple, with slightly curved tapering tips and 
narrow wings. Posterior bristles in groups of two or three, the shaft narrowed at the neck, 
then expanding into a flattened shoulder with the distal edge serrated, and a short tapering 
whip at one border. 
Anterior hooks with a long and minutely denticulate anterior edge and a blunt process 
inferiorly (representing the main fang). Body narrow and translucent. Posterior hooks 
similar but smaller. Tube fixed, vitreous, of great hardness, only curved, not coiled, and the 
aperture with a dorsal spike and two infero-lateral spikes. 
SYNONYMS. 
1761. Serpula triquetra, Linneeus. Fauna Suec., ed. 2, p. 535. 
1768. i " Gunnerus. Norske Vid.-Selsk. Skrift., iv, p. 53, Tab. 11, fig. 14. 
1776. 3 y Muller. Prodr. Zool. Dan., p. 236, no. 2856. 
L779). » tridentata, J.C. Fabricius. Reise nach Norwegen, p. 385 (fide auct.). 
1808. »  triquetra, Montagu. Suppl., p. 157. 
1825. »  serrulata, Fleming. Hdin. Encycl., vu, p. 67, t. cciv, fig. 8. 
»  Vermilia a Idem. Edin. Journ., p. 2438. 
1827. ? Serpula _,, Brown. Illust., pl. u, fig. 8, edit. 2; pl. lviii, fig. 8. 
1836. Serpula crystallinus, Scacchi. Catalogo, p. 18. 
1841. »  triquetroides, Delle Chiaje. Descriz., vol. v, p. 94, and Memor. iv, p. 208, t. Ixvii, figs. 
15 and 16. 
1844. Placostegus crystallinus, Philippi. Arch. f. Naturges., 10th Jahrg., p. 192. 
1845. Serpula serrulata, Johnston. Index, Ann. Nat. Hist., xvi, p. 454. 
1851. »  polita, Sars. Reise 1849, Nyt. Mag., vi, p. 204. 
1854. Vermilia tricuspidata, Morris. Brit. Foss., p. 95. 
1859. Serpula polita, Danielssen. Reise, 1857, p. 124. 
1861-63. Placostegus tridentatus, Mérch. Nat. Vidskr., 3 R., p. 414. 
1864. s politus, Sars. Forh. Vid.-Selsk. Christ., p. 57. 
1867. a tridentatus, Malmgren. Annul. Polych., p. 121. 
1878. 5 erystallinus, Kupffer. Exped. Ostsee “ Pommerania,” p. 152. 
1874. 3 tridentatus, Malm. Annel. Géteborg., p. 1035. 
1878. < “i Hansen. Arch. Math. Naturvid., Tab. in, figs. 1—7, p. 43. 
1879. a re Tauber. Annul. Danica, p. 140. 
1880. sf tricuspidatus, Langerhans. Zeitschr. f. wiss. Zool., Bd. xxxiv, p. 121. 
1884. 3 tridentatus, idem. Ibid., Bd. xl, p. 275, pl. xvi, fig. 39. 
s $3 33 Levinsen. Vidensk. Meddel., p. 198, Tab. ui, fig. 5. 
1889. 5 Grieg. Bergens Mus. Aarb., p. 9. 
1891. ie 5 Appellof. Ibid., p. 8. 
1893. ¥ se Levinsen. “Hauchs” Tog., p. 364. 
Marenzeller. Polych. Grundes, p. 19, Taf. iv, fig. 17. 
tricuspidatus, Sowerb., Lo Bianco. Atti. R. Accad. Sc. Nap., vol. v, no. 11, p. 87. 
1894. Ps tridentatus, Bidenkap. Christ. Vid.-selsk. Forhandl., p. 189. 
1896. . he Appellof. Berg. Mus. Aarb., xin, p. 12. 
a a tricuspidatus, Roule. Camp. ‘ Caudan,” p. 463. 
1897. 3 5 Michaelsen, Polych. deutsch. Meere, p. 188. 
217 
