BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 159 
scarcity of ascidians in this portion of Vineyard Sound, since several of the forms in 
question (Didemnum and all of the species of Amarouciwm) are abundant in this cold 
water, on the stony bottoms close to shore,* and even on Devils Bridge, off Gay Head. 
On the other hand, Molgula arenata (chart 190), likewise a predominantly southward 
ranging form, as judged from known records, occurs chiefly in the western part of 
Vineyard Sound, where its congenial habitat, a sandy bottom, is more prevalent.? 
It would thus seem probable that the temperature factor plays little or no part in 
determining the distribution of ascidians within the limits of our charts, the primary 
factor being the character of the bottom, either directly or in its effect upon the distri- 
bution of marine alge. . ‘ 
In the outlying colder waters, however, where northern representatives of nearly 
every phylum have been met with, we have found a number of ascidians proper to the 
“Acadian” fauna. Such are Halocynthia echinata,’ Ascidia complanata, and the Boltenia 
recorded in the annotated list, all of which species have been dredged,by us at Crab 
Ledge. 
An interesting difference of distribution in relation to depth is revealed by an 
analysis of the records for Amaroucium pellucidum constellatum and A. stellatum. The 
latter was dredged only once at a depth less than 5 fathoms, while in more than 60 per 
cent of the cases it was taken at depths of 10 fathoms or more.? A. constellatum, on the 
other hand, was recorded 15 times from depths less than 5 fathoms, while in over 60 per 
cent of the cases it was taken at depths under 10 fathoms. This form is likewise 
known to occur upon piles, etc., in shallow water, while we have not observed A. stel- 
latum in such situations. : 
The following list comprises all those species which were recorded in our dredging. 
The asterisk has the usual significance. 
? Molgula citrina. Botryllus schlosseri. 
? Molgula koreni. * Perophora viridis (chart 193). 
* Molgula manhattensis (chart 191). * Didemnum lutarium (chart 194). 
? Molgula pannosa. Aplidium pallidum. é¢ 
* Molgula arenata (chart 190). * Amaroucium pelludicum€é (chart 195). 
Eugyra glutinans (chart 190). * Amaroucium pelludicum constellatum¢ (chart 
Halocynthia echinata. 196). 
Boltenia sp. Amaroucium glabrum. ¢ 
* Styela partita (chart 192). * Amaroucium stellatum é (chart 197). 
Styela sp. (Perhaps new.— Ritter). Amaroucium sp. (Perhaps new.—Ritter). 
Ascidia complanata. 
The ranges here stated for the eight commouer species are given for the most part 
on the authority of Verrill (1873) and of Van Name (1910). The statements of the 
latter author have been followed for the compound forms, but for the simple ones no 
data later than those offered by Verrill appear to be available. 
@ It is true that the summer temperature of these shoal inshore waters is somewhat higher than that of the deeper waters in 
the middle of the channel. 
> Eugyra glutinans, another sand-dwelling species occurring in this same region, is however, a predominantly northern form. 
¢ This was likewise taken at Sankaty Head and once in Vineyard Sound. 
4d This notwithstanding the fact that depths as great as this were encountered at only 36 per cent of the stations. 
¢ These five species are among those listed by Herdman as ‘‘unrecognizable Polyclinide.’’ However imperfect the original 
descriptions may have been, these names none the less refer to well-known and readily distinguishable members of our local fauna. 
