732 The American Naturalist. [September,’ 
BIBLIOGRAPHY. 
1. Bonnet.—Oeuvres d’Histoire Naturelle et de Philosophie, 
vol. i, p. 167-336, 1779. 
2. Grabe.—Archiv f. Naturg., vol. x, p. 200, 1844. 
3. Biilow.—Archiv f. Naturg., vol. xlix, 1883. 
4. Robertson— Quart. Journ. Mic. Sci., vol. xv, p. 157, 1867. 
5. Bell—Ann. Mag. Nat. Hist., vol. xvi, p. 475, 1885. 
6. Horst. Pa esc ned. Dierk. Vereniging, 2 ser., D. I, Af. i, 
p. xxxil, 1882. 
7. Fiteh—Eighth Report upon Insects of the State of New 
York, Appendix, p. 204-9, Albany, 1865. 
8. Marsh.—American Naturalist, xxiv, p. 373, 1890. 
` 9. Zeppelin.—Zeit. f. wiss. Zool., xx xix, p. 615-648, 1883. 
10. Claparéde—Les Annélides Chétopods du Golfe de 
Naples, p. 456, 1868. 
11. Brunette—Travaux de la Sta. Zool. de Cette, p. 8, Nancy, 
1888. 
12. Langerhans.—Nova. Acta. K. L. C. D. Acad., vol. xiii, p. 
102, 1879. 
13. Andrews.—Proc. U. S. Nat. Mus., vol. xiv, p. 283, 1891. 
14. Bell.—Proc. Zool. Soc. London, p. 3, 1887. 
15. McIntosh—Challenger Reports, xii, 1885. 
Explanation of Plate. 
Fig. 1. Ctenodrilus monostylos x 124. Zeppelin (9), pl. 36, 
fig. 18. 
Fig. 2. Salmacina incrustans. Claparéde (10), pl. 30, fig. 5F. 
Fig. 3. Ctenodrilus monostylos x 224. Zeppelin (9), pl. 36, 
fig. 19; drawn from a living specimen ; not that shown in fig. 
-` 1, above. 
Fig. 4. Posterior end of Lumbricus terrestris. Robertson (4). 
Fig. 5. Same as fig. 4, but cut open to show intestine and 
dorsal blood vessel. 
Fig. 6. Typhlosyllis variegatus, with two new heads. Langer- 
hans (13). 
Fig. 7. Posterior part of a naiad cut into three pieces and 
forming two heads (?) Bonnet (1), pl. 1’. 
