The Habits and Reactions of a Comatulid, Tropiometra Carinata. 119 



more than 6 or 7 liters. Unlike the comatulids tried in Torres Strait, 

 Tropiometra when fresh from the sea responds to a saturated solution 

 of MgS0 4 in sea-water, like other echinoderms, the whole muscular 

 system becoming relaxed. The response was much less complete if 

 the individual had been for some time in a limited amount of sea- 

 water; probably the presence of CO 2 made the difference. Response 

 to alcohol and formalin was, as in other comatulids, by a contraction 

 first of the dorsal side of the arms and then of the ventral. Only 

 exceptionally, and then by individuals which had been long in tank 

 or aquaria, were the arms cast off. 



SUMMARY. 



The common habitat of Tropiometra at Tobago, Buccoo Bay, is 

 unusual for a crinoid, the bottom being covered with coralline algae 

 and eelgrass, the water shallow, and the comatulids exposed to the 

 full glare of the tropical sun. 



Reactions to light, temperature, salinity, and C0 2 all show Tropio- 

 metra to be remarkably insensitive and hardy. It shows only feeble 

 phototactic reactions, has a temperature range of at least 15 C., a 

 salinity range well over 40 per cent, and withstands a considerable but 

 undetermined amount of COa without injury. 



