Report on the zoological collections made in the Indo-Pacific Ocean ...

;148 COLLECTIONS FEOM MELANESIA.almost black), the differences in the extent to which the papillae aredeveloped, and the comparatively much greater firmness of theintegument of the younger specimens help us to understand how itis that several different names have been given to this widely distributedspecies. On the other hand, it is well to still bear in mindthat our knowledge of Holothurian organization is not yet so completeas to justify us in definitely asserting that fresh differentialmarks do not yet remain to be discovered ; if there are such, theseries now regarded as single may be shown to contain representativesof more than one form.As the only illustration of the spicules appears to be that whichhas been given by Prof. Semper, I have had views made of themfrom the side to show the characters of the free projecting processes,and from below showing the inside of the hemisphere.Port Molle; Port Denison ; Torres Straits; Alert Island (TorresStraits), 17 fms., sand.6. ColocMrus australis.Ludwig, Semper''s Arheiten, ii. p. SS,This species, which is represented by only one specimen from PortMolle (14 fms.), was more richly so in a collection forwarded somethree years ago from Port Jackson by Mr. J. Erazier. I do not,however, find that the suckers are in them brown in colour, whilethe tentacles are rather black and white than brown and yellow.Neither of these are, however, points of any real importance. Ifind, from Mr. Eamsay's collections, that this species is very abundantin Port Jackson.7. Actinocucumis difficilis. (Plate IX. fig. C.)I have had the greatest difficulty in assuring myself of the specificdistinctness of this form from the A. typiea of Ludwig, the variationsexhibited in the present collection impressing one with thenecessity of the greatest care in the delimitation of species.The species may perhaps be most conveniently described bypointing out the several characters by which it is to be distinguishedfrom A. tyjnca. The ambulacral papilhe on the dorsal surface arerare, and the suckers are not in more than four rows for each raythe difterences in the form of the spicules will be best seen by comparingthe figures now given with those drawn by Professor Ludwig.The retractors are inserted rather further back, being found at 24miUim. from the anterior end in a specimen 65 millim. long, andat 22 millim. in one 70 millim. long ; the genital tubes are shorterthan in A. ti/pica, being not more than 15 millim. long in any specimenexamined. The Polian vesicle would also appear to be shorter,being only 7"0 miUim. long in a specimen of 65 millim. length. Itmay be added that the loop of the intestine is exceedingly shortthat the tentacles, which are not always 20, sometimes seem to