212 THE VOYAGE OF H.M.S. CHALLENGER. 



group are strictly littoral, and most if not all occur from between tide-marks to a depth 

 of not more than a few fathoms. 



Two of the new genera in the above-mentioned groups are of special interest. 

 Latreillo2:>sis, of which a single species was taken off the Philippines, forms an interesting 

 connecting link between Homola and Latreillia, inasmuch as it combines the body of 

 the former, with the attenuated limbs and eye-stalks of the latter, thus showing the 

 necessity of placing all three in a single family. The genus Zanclifer has been estab- 

 lished for a curious Raninid taken in shallow water off Bahia, which possesses some 

 interesting structural peculiarities. Originally discovered in the West Indies, upwards 

 of fifty years ago, it was described in a very imperfect manner by its discoverer, de 

 Freminville, who referred it to the fossil genus Eryon. The manifest inaccuracy of this 

 description led to its being ignored by most subsequent writers, and the species was 

 apparently lost sight of till rediscovered by the Challenger. It is sharply distinguished 

 from all other Eaninidea by certain prominent features, and more especially by the form 

 of the eyes, which are so extremely rudimentary as to be scarcely recognisable at first 

 sight. It seems probable that in this case partial loss of vision has been brought about 

 by the animal taking up its abode in subterranean burrows. 



The Paguridea and Galatheidea comprise more than four-fifths of the total number of 

 species in the collection, and the facts connected with their bathymetrical distribution 

 are among the most important discussed in the Report. 



Three new species of Lithodea were taken, all of them in the southern hemisphere. 

 The members of this group were formerly believed to occur only in the shallow water of 

 the northern and southern temperate regions, but deep-sea dredgings, more especially 

 those of the " Talisman," have shown that they extend to the tropics, in which case they 

 are confined to deep water (some of the species reaching a depth of over 1000 fathoms), 

 where the temperature conditions are doubtless favourable to their existence. As Pro- 

 fessor A. Milne-Edwards has pointed out, this unexpected feature in their distribution is 

 not without interest, inasmuch as it shows the possibility of certain forms spreading from 

 the one circumpolar region to the other, and accommodating themselves to the altered 

 environment, in order to obtain the necessary conditions of temjjerature. 



The Pagurodea, or Hermit Crabs, extend to a depth of more than 2000 fathoms. A 

 few of the characteristic shallow- water genera, e.g., Eui^agurus and Paguristes, extend to 

 deep water, but the majority of the abyssal species belong to genera which have either 

 recently, or in the preceding pages, been described as new. In nearly all cases the 

 branchiae of the deep-water forms, while retaining their normal arrangement, exhibit a 

 puzzHng modification of structure. The two collateral rows of flattened leaflets met with 

 on each branchial stem in the gills of the ordinary Pagurids are replaced by a double 

 row of rounded filaments ; in other words, there is a departure from the phyllobranchiate 

 to the trichobranchiate type. It so happens that this condition is the reverse of what 



