VAN NAME: COMPOUND ASCIDIANS. 349 
Comparative Abundance.. 
Macrocllninn patinnn and Botrylloides aurcuni, though widely dis- 
tributed and locally abundant in European waters, are poijrly repre- 
sented in the collections, probably because their range lies chiefly to 
the north and eastward of the region where most of the collecting was 
done. Polycitor kiikcnthali also was collected from few localities, 
and is rare in Europe as well. The deep-water species Leptoclinides 
faeroensis, though represented by comparatively few specimens, must 
grow luxuriantly in some places, judging by the large and flourishing 
colonies it forms. Holozoa clavata, Dideninopsis tencrum, Lisso- 
clinum aureum, and Aplidium pallidum are widely distributed but 
local, and can seldom be found in any considerable quantity, Lisso- 
cliniim aureum being decidedly rare. The remaining seven species 
are all abundant, locally at least, and may be collected in large quanti- 
ties in the favorable places and seasons. ' The extraordinarily luxuriant 
growth of Amaroucium pcUucidum and A. sfellatum in Vineyard Sound 
is mentioned below (pp. 406 and 418), but considering its wide dis- 
tribution and the large number of stations where it is very common, 
Amaroucium glabrum is probably really more abundant than any of 
the others. 
Descriptions of Species. 
The numbered dredging and trawling stations mentioned are those 
of the United States Fish Commission. 
The classification and nomenclature is substantially that of Hart- 
meyer (1908b, 1909). The writer has not departed from it in any case 
without a full explanation of the reasons for so doing. In Hartmeyer's 
system, through conformity to the international rules of nomenclature, 
several of the familiar generic names of compound ascidians are 
abandoned or applied to other genera. The genus Didemnum in the 
sense hitherto usually employed becomes Trididemnum Delia \^alle, 
1881, white the name Didemnum Savigny, 181G, is applied to the 
genus that has been known as I.eptoclinum. The name Leptoclinum 
Milne-Edwards, 1S41, replaces Diplosoma Macdonald, 1858. Dis- 
taplia Delia Valle, 1881, becomes Holozoa Lesson, 1830. The family 
names Distomidae and Polyclinidae are replaced by Polycitoridae and 
Synoicidae, respectively. Where the new names seem likelv to cause 
