ETC. 403 



it would seem difficult for them to digest it, or get much nutriment from. 

 it. The supply is certainly sufficiently abundant. 



A third species of this genus, and much more beautiful than either 

 of the preceding, is also common on rocky bottoms. This is the Ama- 

 rcecium constellatum Y. (p. 388,) which has already been described as 

 occurring on the piles of the wharves. In deeper water, attached to 

 rocks, it grows to a larger size, forming thick, hemispherical or cake- 

 shaped masses or crusts, sometimes becoming somewhat mushroom-like 

 by the upper parts growing out beyond the central attached portion, 

 which then becomes a short and broad peduncle. It can be easily 

 distinguished from the last on account of its brighter colors, the general 

 color inclining to orange, and by the more irregular and complicated 

 clusters of zooids. It is less abundant than either of the two preceding. 



Two other species of compound Ascidians are also abundant in this 

 region, as well as farther north. These belong to the genus LeptocUnum ; 

 they form thin, irregular, often broad, white, or salmon-colored incrus- 

 tations over the surfaces of the rocks, shells, and other ascidians ; these 

 crusts are of a firm, coriaceous or gritty texture, and have a finely 

 gra unions surface. Under the microscope they are seen to be filled 

 with small, nearly globular particles of carbonate of lime, from which 

 points project in every direction. The zooids are very minute and 

 are scattered over the surface in large and scarcely distinct groups, 

 which have, however, a common cloacal orifice in the middle, but the 

 several cloacal tubes or channels leading to each central orifice are 

 long, with many crooked branches, reminding one of miniature rivers, 

 and the zooids are arranged along these ducts and their branches. 

 One of these species, the LeptocUnum alhidumjis easily distinguished 

 by its chalky white color -, the other, L. luteolum, is buff or salmon- 

 color. It is possible that the last may even prove to be only a colored 

 variety of the former, but the very numerous specimens that I have 

 collected and examined, in the living state, both in the Bay of Fundy 

 and Vineyard Sound, do no not warrant their union. In these locali- 

 ties both forms are about equally common, but near New Haven the 

 L. luteolum has not yet been met with, though the other is not uncom- 

 mon. 



The Bryozoa are very abundant on rocky bottoms at all depths. 

 Some of these incrust the rocks directly, like the Escliarella variabilis^ 

 {\). 312,Plate 'XXXlll^fig.2oQ]) Alcyonidiumliirsutum ; Uscharipora punc- 

 tata, &c. ; but even these seem to prefer other locations, and by far the 

 greater number occur attached to algae, hydroids, ascidians, and dead 

 shells. A large part of the species occur also in rocky pools at low- 

 water mark, or attached to the Fuci and other sea-weeds between tides, 

 or to the under sides of stones laid bare by low tides, and have, con- 

 sequently, been previously mentioned. Others which have not yet been 

 detected on the shore will doubtless be found there by more thorough 

 search. 



