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 t'he 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 arenata ' ' 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. B. 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. 



