314 
PACIFIC SCIENCE, Voi. VIII, July, 1954 
ventral ridge; it is absent in largest specimens; 
one lateral attachment organ on each side just 
behind angle of mouth. Muscles: Number va- 
ries, in POFI specimens ranging from 10 on 
one side and 11 on the opposite side to 12 
and 13, respectively; muscles usually unequal 
in number on opposite sides; in POFI spec- 
imens, all body muscles irregularly continuous 
dorsally and connected dorsally by muscle 
strands except the last one, all interrupted 
rather widely ventrally (according to the fig- 
ures of Traustedt, 1885, and Thompson, 1948, 
however, M I and II are distinct muscle 
bands); the last muscle much broader than 
other muscles; M C broad, continuous dors- 
ally, widely interrupted ventrally. Ciliated 
groove, ganglion and eye: Ciliated groove elon- 
gate, straight, simple, located between M I 
•and M C or under M C; ganglion and eye 
located far posteriorly, under M IV or V; eye 
a modified horseshoe (see Metcalf, 1918, fig. 
39) with pigment at base and at each tip. 
Viscera: Gut moderately compact, in condi- 
tion E (Ihle and Ihle-Landenberg, 1933); 
stolon forming a weak spiral, coursing ante- 
riorly, bending and coursing posteriorly on 
left side of gut. 
AGGREGATE FORM: More than 10 specimens 
examined with length range of 2 (stolon in- 
dividual)-4l mm. (Fig. 21). Test: As with the 
solitary form, the aggregate form has been 
figured well by Traustedt (1885), Brooks 
(1893), and Apstein (1894(3). TraustedtT fig- 
ure, unfortunately, is of a dissected specimen, 
thus does not show the dorsal surface of the 
test. Test firm, asymmetric; middorsal de- 
pression thin, limited by weak grooves; dorsal 
limiting ridges on either side of depression, 
one always farther away from dorsal depres- 
sion than other; these ridges continuing an- 
teriorly into a circular ridge ringing the mouth 
widely; circular ridge on this side continuing 
posteriorly as lateral ridge ending after turn- 
ing ventrally near level of gut; a prominent 
circular projection posteriorly over gut, flat 
on top and ridged; gut swelling and chin 
prominent; ventrolateral ridge not serrated 
except on posterior tip (no equivalent ridge 
on opposite side of body) ; on opposite side 
a ventrolateral ridge (equivalent to lateral 
ridge above), serrated; in ventral view, a 
prominent midventral ridge over gut swelling 
disappearing anteriorly, forming a small pos- 
terior projection; all ridges mentioned except 
ventrolateral ridge on one side (left side in 
figures) and midventral ridge rather strongly 
serrated; thus six longitudinal ridges, one 
anterior circular one, and one posterior one 
below the cloacal siphon; attachment organs 
usually six — one large one at each end, one 
smaller circular one just anterior and poste- 
rior, respectively, to the latter, and two smaller 
circular ones midventrally. Muscles: Six body 
muscles, all interrupted ventrally, continuous 
dorsally; M I-IV forming a group dorsally, 
M V and VI independent; M V wider than 
first four, M VI much wider than V; M C 
broad, anterior part continuous middorsal- 
ly; posterior part branching off from latter, 
interrupted dorsally. Ciliated groove: Moderate- 
ly elongate, simple. Viscera: Gut compact, 
in condition E (Ihle and Ihle-Landenberg, 
1933); endostyle sinuous; two to five, usual- 
ly four embryos present. 
Genus Thetys Tilesius, 1802 
Solitary form with 16-22, aggregate form 
with 5, weakly developed body muscles which 
are widely interrupted ventrally. Some of them 
are also laterally interrupted. Test firm, with 
many large spines over surface but without 
serrated ridges. 
One species, Thetys vagina, 
Thetys vagina Tilesius, 1802 
Figs. 22a-d, 2'ia-d 
Dagysa notata [part.] Gmelin, 1791: 3131. 
Thetys vagina Tilesius, 1802: 150; Ihle, 1935: 
527-529; Tokioka, 1937: 224; Thompson, 
1948: 136. 
Salpa tilesii Cuvier, 1804: 375. 
Dagysa strumosa Home, 1814: 71. 
Salpa costata Quoy and Gaimard, 1824: 504. 
