. Bulletin - United States National Museum. Science. 300 BULLETIN" 93, UNITED STATES NATIONAL MUSEUM. and tapering below. The articular ridge of the tergum is very small, and the articular furro^v is narrow. The bilateral asymmetry of the opercular valves, though not conspicuous, is noticeable in some of this lot (fig. 83). I have often observed such asymmetry in this and other species of Chthmnalus, but never in any other genus of Balanidce or Chthwrnalkla. The specimen I dissected from Ocean City differs a little from that taken at station 2004 in the second cirri, as I have noted above
. Bulletin - United States National Museum. Science. 300 BULLETIN" 93, UNITED STATES NATIONAL MUSEUM. and tapering below. The articular ridge of the tergum is very small, and the articular furro^v is narrow. The bilateral asymmetry of the opercular valves, though not conspicuous, is noticeable in some of this lot (fig. 83). I have often observed such asymmetry in this and other species of Chthmnalus, but never in any other genus of Balanidce or Chthwrnalkla. The specimen I dissected from Ocean City differs a little from that taken at station 2004 in the second cirri, as I have noted above, but not in tiny other character of the mouth or cirri. Excepting Darwin's Charleston record for fragllis, the only pub- lished notice of Chthamtdus on our Atlantic coast is contained in an article by Dr. F. B. Sumner (1909). Specimens identi- fied by Doctor Sum- ner as C. stellatus var. fragilis were found to occur in consider- able numbers on Pen- zance Point, along the shore of Woods Hole Passage. Further search has revealed its presence on the piles of piers at Woods Hole, New Bedford, and Vineyard Haven, and on rocks at Nobska Point, Nonamesset Island, and the shore of Buzzards Bay near Woods Hole. It is probable, indeed, that its local distribution is very general. At the last-named point this species seems to be particularly abundant. It extends consider- ably higher up on the bowlders than does Balanus halanoides, with which however, it is associated at a lower level. It thus occurs at points which must be uncovered by the tide for the greater part of the time. In local waters, so far as I have seen, Chthamalus never grows in such dense clusters as does Balanus halanoides, and indeed it appears unable to compete very successfully with the latter in its proper zone. Like its associate, it is a strictly littoral form and probably does not extend below tidal limits. The local examples, in large part at least, seem to belong to the variety fragilis of Darwin, as did the sp
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