170 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The species of Zen omet rinse, Pentametrocrinidfe, :mcl Atelecrinidse are ex- 

 tremely brittle, so brittle indeed that in many the cirri and the arm tips are quite 

 unknown. In these three groups it is especially noticeable that the arms are rarely 

 lost at the first syzygy, but almost always at the second or third or beyond. 



The species of Bathymetrinse are mostly very brittle, and in many of them the 

 cirri and the outer portions of the arms have never been seen. Trichometra and 

 Thaumatometra stand rather apart from the other genera in being much less sub- 

 ject to mutilation during capture. In the case of Trichometra this relative tough- 

 ness has almost the value of a generic character in serving to differentiate the 

 species from those of the very closely related but extremely brittle Hathrometra. 



The species of the genera of Heliometrina?, though very large, are decidedly 

 brittle, and good specimens are almost impossible to secure. The species of Solano- 

 metra seem to be rather less fragile than their allies. 



The species of the genera Thysanometra and Goccoinetra^ included in the 

 Thysanometrinse, are rather less brittle than most macrophreate types. 



In the Arctic and north Atlantic oceans species of Heliometra and of Hathro- 

 metra are often dredged together, and when this occurs Heliometra is seen to be 

 much less fragile than the smaller Hathrometra. In the Okhotsk and Japanese 

 seas Heliometra and Thaumatometra occur together and are often intermingled in 

 the dredge, and here the small Thaumatometra is found to be much less fragile than 

 the larger Heliometra. 



The tendency of the comatulids to cast off their appendages, pinnules, arms, 

 and cirri, when taken from the water or otherwise placed imder unfavorable sur- 

 roundings, renders them very difficult to preserve satisfactorily. But I have found 

 that self-mutilation can largely be prevented by quickly lifting the animals and 

 plunging them at once into very strong alcohol or very hot water. If one attempts 

 to kill them slowly in the usual way, in weak alcohol or in fresh water, they are 

 certain to disintegrate into small fragments. 



Long ago the Japanese fishermen discovered the high commercial value of the 

 "bird's foot" {M etacrinus rotundus) in the European market, and they soon found 

 that " birds' feet " could be preserved without the loss of their arms if when they 

 were brought to the surface the arms were brought together and bound in place 

 with a strip of cloth. This in most cases prevents the creatures from breaking off 

 the arms, as they are certain to do if allowed to bend them outward and downward 

 toward the stem. 



Almost all the students of the comatulids except Sars have considered the 

 syzygies as locus minoris resistentia^ where fracture of the arm automatically takes 

 place when the arm is seized, as the result of some special weakness. 



My experience with living comatulids and with preserved specimens has led 

 me to agree witli Sars; the syzygies under ordinary circiunstances are at least as 

 strong as the muscular articulations, as anyone may prove for himself by breaking 

 up crinoid arms; and those who have separated the brachials of a crinoid arm by 

 means of caustic have always found that the syzygies are by no means regions 

 of lessened resistance, for they are as a rule the last joints to come apart, and often 



