Crustacea.] SUBANTARCTIC ISLANDS OF NEW ZEALAND. 609 



Genus Halicarcinus, White, 1846. 

 Distribution. — Subantarctic seas frenerallv. 



Halicarcinus planatus (Fabi.). 



Cancer flanatus, Fabr., Ent. Syst., t. 11, p. 446, 1793. Halicarcinus flanatus. 

 White, Ann. & Mag. Nat. Hist., xviii, p. 178, pi. ii, fig. 1, 1846 ; Miers, 

 Cat. N.Z. Crust., p. 49, 1876 ; Haswell, Cat. Aust. Crust., p. 114, 1882 ; 

 Filhol, " Mission de I'lle Campbell," p. 396, 1885 ; Stebbing, P.Z.S., 

 1900, p. 524, pi, xxxvi6, 1900; Hodgson, "Southern Cross" Crust., 

 p. 231, 1902. 



This species was found during the expedition to be very abundant between 

 tide-marks in Perseverance Harbour, Campbell Island ; and numerous other speci- 

 mens were brought to me from various parts of both Auckland and Campbell Islands. 



It is evidently a species of wide circumpolar distribution, and has been many 

 times referred to and described under different names, and even yet there are various 

 points of uncertainty that have not been cleared up. A full discussion of most of 

 these will be found in Mr. Stebbing's paper quoted above. 



In his " Mission de I'lle Campbell " Filhol has distinguished H. flanatus. White, 

 and H. tridentatus (Jacq. et Luc.) from one another mainly by certain small characters 

 of the tridentate front. This separation of the two species is upheld by Lenz, and 

 by the writer of the account given of the Crustacea of the " Mission du Cap Horn." 

 So far as the specimens at my disposal go, they certainly confirm Filhol' s statements 

 as to the existence of slight differences between the two forms ; and this is also con- 

 firmed by the geographical distribution, for all the specimens in my possession from 

 the Auckland and Campbell Islands belong to H. planatus as understood by Filhol, 

 while all those from New Zealand itself and from Chatham Island, belong to H. tri- 

 dentatus as described by him. The differences are, however, only slight, and whether 

 they are sufficient for specific separation is another question. Personally, I am, on 

 the whole, inclined to consider the two forms as merely local varieties or subspecies of 

 a widely distributed species. The differences are briefly as follows : In H. planatus 

 the posterior lateral tooth on the margin of the carapace is always present and more 

 or less acute, though situated a little below the level of the carapace. In the tridentate 

 front the lateral teeth are somewhat widely separated from the median one, and they 

 are produced a little downwards at the sides, so as to be slightly concave on the 

 inner surface, and in this way a slight recess is formed below the median tooth, in which 

 the antennae rest, and there is practically no ridge on the epistome to divide the recess 

 into two portions. In H. tridentatus, on the other hand, the three teeth of the front 

 lie closer together and more in the one horizontal plane, and the lateral teeth are 

 flattened both above and below, so that there is no recess formed below the median 

 tooth, and, on the contrary, there may even be a slight ridge on the epistome. In 

 this form also both the teeth on the lateral margins of the carapace are obsolete, 

 even the posterior one generally showing as little more than a slight projection. 

 These differences, with the exception perhaps of the presence or absence of the 

 posterior marginal tooth, readily escape observation, and naturally they are less 

 marked in immature specimens. Consequently, it is practically impossible to tell 

 from the descriptions of previous authors which of these two forms they had before 

 40— S. 



