306 
PACIFIC SCIENCE, VoL VIII, July, 1954 
\ld). Test: Glutinous, dorsally and laterally 
thin, ventrally thickened especially over the 
gut as gut swelling; from anterior point of 
gut swelling, two weak ridges lacking spines 
coursing shortly anteriorly and posteriorly on 
ventral surface of gut swelling; anteriorly a 
sparsely spined ridge encircling base of ven- 
tral lip; chin weakly developed; attachment 
organs absent; a varying number of white 
patches of thickened test most prominent 
posteriorly, especially over the gut, arranged 
in three rows on each side: (1) a dorsolateral 
row, (2) a lateral row, and (3) a ventrolateral 
row at edge of thickened ventral test con- 
tinuing with patches over gut. Muscles: Eight 
(sometimes nine, as described by Sewell, 
1926) body muscles, some of which may 
divide into two branches laterally; M I-IV 
approaching, fusing, or joining by means of 
fine strands of muscle dorsally, varying con- 
siderably (Eig. \lb-d) \ remainder of muscles 
usually equally separate from ane another ex- 
cept X, which may approach M VIII dorsally; 
all body muscles extend rather far ventrally; 
some may be fused, but usually are separate. 
Ciliated groove: Simple, elongate, straight or 
slightly bent. Viscera: Gut compact, in con- 
dition E of Ihle and Ihle-Landenberg (1933) 
(Fig. 17^); stolon club-shaped, straight (or 
undulating according to Thompson, 1948); 
transverse ribs of gill touching one another 
dorsolaterally; tapering sharply and becoming 
rather far separated ventrally. In species of 
Salpa, these ribs are separate along their entire 
length and taper gradually toward the ventral 
surface (Fig. 16). 
AGGREGATE FORM: Over 10 specimens ex- 
amined, with length range of 6-1 6 mm. (Fig. 
17/). Test: Flabby, without permanent ridges 
or grooves; one anterior and one posterior 
asymmetric projection, which are usually short 
and stumpy, but may be elongate as in Fig. 
Ilf. Eight attachment organs present accord- 
ing to Stiasny (1926), but only six were visible 
in POEI specimens. Muscles: Five body mus- 
cles; M I-III fused dorsally as are M IV and 
V ; in all POFI specimens the two groups are 
joined dorsally (but may be distinct, accord- 
ing to other investigators) ; muscles extending 
rather far ventrally. Ciliated groove: Slightly 
arched, simple. Viscera: Gut compact, in con- 
dition E of Ihle and Ihle-Landenberg (1933); 
embryo on right side between M IV and V; 
gill as in solitary form. 
This salp has been studied by many in- 
vestigators, but only Brooks (1893) and, es- 
pecially, Sewell (1926) have shown any of the 
great variation in muscle arrangement that 
occurs in the solitary form. The usual de- 
scriptions point out only that M I-IV ap- 
proach or touch dorsally, the rest remain 
separate. The actual muscular arrangement 
may differ considerably from this condition 
(Fig. llh-d). In regard to the test of the 
solitary form. Brooks (1893), Sewell (1926), 
and Stiasny (1926) described seven longitud- 
inal ridges — two dorsal, two lateral, and three 
ventral — as well as a posterior ridge. In all 
specimens I have examined, however, there 
are only two longitudinal ventral ridges pres- 
ent, and they are much shorter than those 
described by the above-named investigators. 
Evidently, there is also a rather large amount 
of variation in test structure. Almost all spec- 
imens, both aggregate and solitary, in the 
POEI collections are separated from their 
tests. In only a few individuals did the tests 
remain on the animals. I was unable to find 
the ridges described by Stiasny (1926) on the 
test of the aggregate form. 
Genus Ritteriella Metcalf, 1919 
Solitary form with 10 to 24 body muscles, 
all of which are ventrally interrupted, except 
in R. amboinensis the first three or four form 
complete rings. Aggregate form with six body 
muscles that form groups dorsally. Transverse 
ridges of gill bar are separated from one 
another by a distance greater than 0.5 the 
width of the gill bar. Solitary form possesses 
a blood-forming organ. 
Two species, Ritteriella amboinensis (type) 
and R. picteti. 
R. picteti and R. amboinensis were first de- 
