550 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
1908. Styeln riistica Bjerkan, Tromsoe Mus. Aarshefter, no. 25, pp. 63, 115. 
1909. Tethyum rusiicmn Hartmeyer, Bronn's Tier-reich, vol. 3, suppl., p. 
1360. 
1910. Tethyum rusticum Hartmeyer, Danmark-Expoditionen, vol. 5, p. 234. 
1912. Tethyum rusticum Hartmeyer, Vidensk. Meddel. Naturhist. For. 
Kjobenhavn, vol. 63, p. 266. 
1912. Tethyum rusticum Hartmeyer, Sitzungsb. Ges. Naturforsch. Freunde, 
1911, no. 10, pp. 439, 440. 
1:^ ot Ascidiarustica Couthouy, 1838; Gould, 1841; DeKay, 1843; Binney, 1870. 
Ordinary form of the body in well developed indi\'iduals elongated, 
larger at the anterior than at the posterior (attached) end. Apertures 
situated on small (often inconspicuous) elevations; the branchial 
aperture terminal, the atrial a little back from the end. Yet low 
rounded individuals attached bv a broad base also occur, and some 
Text-fig. 30. — - Tethyum rusticum (Linnaeus). X 1.4^- 
are even greatly flattened dorso-ventrally so that they have the form 
of a very flat cone, the test spreading out over the surface on which 
they are attached beyond the border of the body proper. A more or 
less conspicuous pointed projection of the test, sometimes 5 mm. or 
more long, is very frequently present between the apertures and 
appears to be characteristic of the species when present, but it is 
often entirely wanting. Surface of the body very strongly wrinkled 
in a transverse direction. These wrinkles generally break up on the 
anterior part of the body into irregular rounded prominences. 
Test thick, especially near the apertures, and of tough leathery 
consistency. Color reddish or brownish, especially on the anterior 
part of the body, retaining this even in many preserved specimens. 
Measurements of largest specimens studied: 46 mm. to 55 mm. long 
and 25 mm. in dorso-ventral diameter. The species is generally 
