80 Papers from the Department of Marine Biology. 
soft flesh of the dise or by clasping the pinnules or arms of the crinoid. 
The chelz are less effective for maintaining a hold than the thoracic 
legs, but it is to be noticed that these can not be said to be specially 
modified for this purpose. They are provided with two sharp claws, 
but this provision is also made in cases where the alpheid has no such 
commensal habits. 
When removed from the crinoids they swim about very rapidly, but 
return as soon as possible to the shelter of the host, and cling to it as 
before. They exhibit reactions to light and touch in a very marked 
manner. Alpheids placed in a glass vessel always cluster together on 
the side of the vessel opposite from the light. Besides being negatively 
heliotropic, they are strongly thigmotropic, for when the finger is 
introduced into the water it is instantly embraced by the thoracic legs 
of the alpheid. In the absence of any foreign object, the alpheids 
embrace one another, so that a number left together in a vessel soon 
look like a mass of swarming bees. 
There seems to be a limited faculty of colour change. One individual 
with wide stripes of pigment became lighter toward night, darker again 
at day. Unfortunately I did not make any extended observations on 
this point. 
Synalpheus comatularum (Haswell). (Plate 1, Fig. 1.) 
Alpheus comatularum, Haswe.u, Proc. Linn. Soc., N.S. Wales, vol. 6; Catalogue of the Australian 
Stalk and Sessile Eyed Crustacea, Australian Mus., pp. 189-90. 
This species was dredged in a few fathoms of water in Albany Passage, 
near Cape York, during the cruise of H. M.S. Alert. ‘‘They were 
invariably found clinging to the arms of a species of comatulid to which 
their markings gave them a general resemblance.”’ It was also obtained 
during the voyage of the Challenger, in neighbouring waters and off 
Ceylon, by Professor Herdman. 
We did not find this form at Murray Island, but during a visit to 
the western Islands of Torres Straits, in the early days of November, I 
obtained it in 3 to 5 fathoms off the great reefs lying north of Mabuiag 
Island. With the greatest kindness, Mr. Walker, managing director 
of the Papuan Industries Co., Ltd., put the company’s schooner Dogai 
at my disposal and, with three divers from Badu in addition to the 
ordinary crew, I spent a couple of days on the Mabuiag pearling grounds. 
For an hour or more at slack tide the most wonderful crinoids were to be 
collected by diving. The species so common at Murray Island (Coman- 
thus annulatum) was the dominant form here, but represented by indi- 
viduals even larger and more splendid in colour than those inhabiting 
the reefs of the Murray Islands. 
S. comatularum is markedly larger than S. brucei and is stouter in 
general appearance. But the resemblance in colouration and habits is 
so close as to suggest specific identity until the peculiar form of the 
