BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 1 59 



scarcity of ascidians in this portion of Vineyard Sound, since several of the forms in 

 question (Didcmnum and all of the species of Amaroucium) 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, Molgida arcnata (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. 6 



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 alga. 



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 constellalum 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. 



Botxyllus schlosseri. 



* Perophora viridis (chart 193). 



* Didemnum lutarium (chart 194). 

 Aplidium pallidum.* 



* Amaroucium pelludicum* (chart 195). 



* Amaroucium pelludicum constellatum' (chart 



196). 

 Amaroucium glabrum.* 



* Amaroucium stellatum* (chart 197). 

 Amaroucium sp. (Perhaps new. — Ritter). 



? Molgula citrina. 

 ? Molgula koreni. 



* Molgula manhattensis (chart 191). 

 ? Molgula pannosa. 



* Molgula arenata (chart 190). 

 Eugyra glutinans (chart 190). 

 Halocynthia echinata. 

 Boltenia sp. 



* Styela partita (chart 192). 

 Styela sp. (Perhaps new. — Ritter). 

 Ascidia complanata. 



The ranges here stated for the eight commoner 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. 



a It is true that the summer temperatureof these shoal inshore waters is somewhat higher than that of the deeper waters in 

 the middle of the channel. 



b Eugyra glutinans, another sand-dwelling species occurring in this same region, is however, a predominantly northern form. 



c This was likewise taken at Sankaty Head and once in Vineyard Sound. 



<• 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 Polyclinidae." 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. 



