156 BULLETIN OF THE BUREAU OF FISHERIES. | 
distribution was Didemnum lutarium Van Name, which was taken at 99 of the regular 
dredging stations; thus not a single species was taken with sufficient frequency to appear 
in the list of those recorded from one-fourth or more of the entire number of stations. 
Only eight species were taken at as many as 10 of the stations. 
As in the case of some other groups, certain of the earlier identifications by the col- 
lectors in the field were made with a confidence which did not afterwards seem to us 
justified. During the later seasons, accordingly, we preserved for reference to specialists 
a much larger proportion of the specimens taken. The only instances of ambiguity in 
our records, which seem worth considering, relate to the species of Amaroucium and to 
Molgula arenata. ‘The former were commonly identified in the field by means of a super- 
ficial examination. Subsequent information leads us to believe that such identifications 
were for the most part correct; since the commoner, at least, among our local species 
are in most cases readily distinguishable by obvious characters. The small, sand-covered 
solitary ascidians, taken in the western portion of Vineyard Sound, were at first referred 
by us to a single species, Molgula arenata. We were informed by Prof. Ritter, however, 
that another of our local species, Eugyra glutinans, is superficially very similar to the 
former, and that, in the case of preserved specimens, dissection is necessary in order to 
distinguish between the two. Both species have been determined by Prof. Ritter in the 
material submitted to him; so that we feel confident in listing both of them for the 
western part of Vineyard Sound. On the other hand, it is more than possible that some of 
our earlier records for ‘‘Molgula arenaia”’ refer in reality to Eugyra glutinans, while some 
of those for the latter species depend upon an assumed specific identity between specimens 
which were hastily examined and others which had been authoritatively determined. 
In view of this uncertainty, it has been thought best to plot but a single chart for these 
two species, denoting by the stars of solid black those stations from which Molgula 
arenata was recorded, and by the open stars stations from which Eugyra glutinans was 
recorded. 
It is thought likely that errors of omission have been relatively infrequent in our 
records, since few of the local species, so far as known, are minute or inconspicuous. It 
is not unlikely, however, that some of the smaller sand or mud covered solitary ascidians 
may have escaped us, and it is possible that certain less common species (e. g., of Mol- 
gula) have been confused with the more familiar ones and recorded along with the latter. 
We are indebted to Prof. W. E. Ritter, of the University of California, for identifying 
a large number of the simple ascidians, and to Dr. W. G. Van Name, of New Haven, 
for identifying many of the compound forms. To these same authorities we are like-_ 
wise indebted for criticizing the manuscript relating to each of these respective subdi- 
visions, and we have adopted the classification and nomenclature advised by them. 
Prof. Ritter expresses himself as being skeptical regarding the identity of many of the 
Atlantic coast species, and some of his determinations have been made with no great 
confidence. In such cases the doubtful character of the identification has been indicated 
in the list. Dr. Van Name has felt himself justified in making two rather radical changes 
respecting the genera Amaroucium and Leptoclinum (Didemnium). (See faunal cata- 
logue, p. 731-733). 
To Prof. W. A. Herdman, of Liverpool University, we are indebted for suggestions 
and advice relative to this group during the later stages of the writing of this report. 
