BULLETIN 39, UNITED STATES NATIONAL MUSEUM. [24] 



Again, as a reasonable degree of motion in the water brings to 

 sedentary animals a larger supply of food than would otherwise be 

 within their reach, we usually find points and headlands, or islets, 

 washed by marine currents far richer in species than those beaches 

 subject only to the ordinary ebb and flow of the tide. 



Places where fishermen draw their seines are apt to afford specimens 

 accidentally brought in from deeper water. The haddock and some other 

 fishes live partly on mollusks, and therefore the bits of beach where 

 fish are cleaned often repay a search, in spite of incidental annoyances 

 common to such places. 



The late Dr. A. A. Gould had a regular understanding with certain 

 fishmongers that they were to empty the paunches of their haddock 

 into a bucket of clean water, which was afterward strained o&, the 

 debris affording many rarities which could be obtained in no other 

 way. The crops of sea ducks are often crammed with small bivalves, 

 such as Nucula and Leda. Among other facilities for collecting which 

 the markets of a large city afford, apart from the supply of edible 

 species brought for sale, may be mentioned the mud which remains in 

 ■ the barrels in which oysters are brought to market. This will often 

 afford a great many small species if washed and sifted. 



Among other out-of-the-way places where rare and singular mollusks 

 may be obtained are the burrows of crustaceans which are frequently 

 inhabited by species of Lepton. This genus appears to be frequently 

 commensal in its habits. Around the mouth and in the channels which 

 radiate from that aperture, in such Echini as Hemiaster, a small com- 

 mensal species of Lepton is frequently found. A burrowing crustacean 

 {Gehia pugettensis Dana), living on Puget Sound and the coast of British 

 Columbia, frequently carries under its abdomen a species of Lepton, 

 attached to the crab by its byssus, as a lady carries a chatelaine bag 

 at her belt^ The margin of the shell io curved to fit the rotundity of 

 its host, and the mollusk has not been found alive in any other situa- 

 tion. A minute hyaline gastropod (StUifer) is an habitual parasite of 

 starfishes, living half imbedded in the tissues, from which it sucks the 

 juices. Another gastropod [Tliyca) is more strictly commensal, and 

 establishes itself near the anal opening of its echinoid host, from whose 

 ejecta it is supposed to obtain sustenance. Very similar species be- 

 longing to the same family were semiparasitic on many paleozoic 

 crinoids, growing as their host grew, remaining permanently in the 

 same spot, and frequently inducing distortion in the echinoid thus rid- 

 den. A still more extraordinary case is that of Entoconcha mirahilis, a 

 degraded mollusk which is an internal parasite of Synapta, a worm-like 

 organism found on sand beaches. The Entoconclia is found as a sac- 

 shaped mass in the intestine of the Synapta, only recognizable as a 

 mollusk by the development of its eggs, which pass through the usual 

 moUuscan stages, while the larval animal possesses a small shell, after- 

 ward lost, as in the case of many Tectibrauchs. The small gastropods 



