VAX NAME: SIMPLE ASCIDIANS. 549 
A. Branchial sac with but one fold on each side; two gonads on right 
and one on left side morlenseni. 
B. Branchial sac with four folds on each side; gonads rather numerous 
(often six or eight on one side). 
a. Internal longitudinal vessels chiefly confined to folds of branchial 
sac; body sand-covered molle. 
h. Internal longitudinal vessels numerous on interspaces as well as 
on folds. 
Body flattened dorso-ventrally; surface smooth; gonads nu- 
merous on both sides of body. (Northern in distribution.) 
finmarkiense. 
Body elongated, attached by posterior part; surface much 
wrinkled; gonads two on left side, five or more on the right. 
(North Carolina, etc., not known from New England.) 
plicatimi. 
Tethyum rusticum (Linnaeus). 
PI. 59, fig. 89-91; PI. G9, fig. 138; text-fig. 30. 
1767. Ascidia rustica Linnaeus, Syst. Nat., ed. 12, vol. 1, pt. 2, p. 1087, no. 5. 
1842. Ascidia rustica + A. monoceros Moller, Naturhist. Tidsskr., vol. 4, 
p. 95. 
1867. Cynthia condylomata Packard, Mem. Boston Soc. Nat. Hist., vol. 1, 
p. 277. 
1870. Cynthia condylomata Binney, Gould's Invertebrata of Massachusetts, 
p. 19, pi. 23, fig. 324. 
1870. Cynthia condylomata Dall, Proc. Boston Soc. Nat. Hist., vol. 13, p. 255. 
1871. Cynthia monoceros Verrill, Amer. Journ. Sci., ser. 3, vol. 1, p. 93. 
1872. Cynthia monoceros Verrill, Amer. Journ. Sci., ser. 3, vol. 3, p. 213. 
1874. Cynthia monoceros Whiteaves, Amer. Journ. Sci., ser. 3, vol. 7, p. 5. 
1879. Halocynthia rustica Verrill, Bull. U. S. Nat. Mus., no. 15, p. 147. 
1879. Halocynthia rustica Verrill, Proc. U. S. Nat. Mus., vol. 2, p. 197. 
1891. Cynthia monoceros Packard, Labrador Coast, p. 396. 
1901. Halocynthia rustica Whiteaves, Geol. Survey Canada, pub. no. 722, 
p. 268. 
1903. Styela rustica Hartmeyer, in Romer and Schaudinn, Fauna Arctica, 
vol. 3, pt. 2, p. 217, pi. 5, figs. 2, 3. 
1906. Styela rustica Redikorzew, Trav. Soc. Nat. St. Petersbourg, vol. 37, 
pt.l, pp. 154,308, 310. 
1907. Styela rustica Redikorzew, Ann. Mus. Zool. Acad. St. Petersbourg, 
vol. 11, pp. 134, 151-153. 
1907. Styela rustica Redikorzew, Zool. Anzeiger, vol. 31, p. 521. 
1908. Styela rustica Redikorzew, Trav. Soc. Nat. St. Petersbourg, vol. 39, 
pp. 20, 25, 42. 
1908. Styela rustica Bjerkan, Rept. Second Norwegian Arctic Exped., no. 14, 
p. 6. 
1908. Styela rustica Redikorzew, Mem. Acad. Imp. Sci. St. Petersbourg, 
ser. 8, cl. phys.-math., vol. 18, no. 11, p. 29, pi. 2, fig. 28. 
