396 KEY. T. E. E. iSTEBBING ON AMPHIPODA FROM 



other hardly ever. The clear division of the family into two groups hy the palp of the 

 maxillipeds is brought to nought. It is still true that there are some of the genera in 

 Avhich the joints of tlie palp in question are four, and others in which they are only 

 three, but forms are uoav known in which they are not properly either three or four, but 

 rather three and a fraction {ParorcliesUa). 



The anomalous family of the Phliadidai, with which this paper is next concerned, was 

 introduced to scientific notice by that great pioneer in the zoology of the coast-line, 

 Colonel Montagu. It was probably at Salcouibe, in South Devon, that he found the 

 typical species. To this he gave the name of Oniseus testado, indicating by the generic 

 name that he made the cot unnatural mistake of supposing it to be an isopod. Some of 

 its since found congeners have an even more striking likeness to some of the Isopoda. 

 All the Serolidfe are broad and flat, but in them the tortoise-like and chiton-like appear- 

 ance is generally impaired by projecting appendages. On the other hand, a New Zealand 

 isopod genus, Plakarthrium Chilton, subsequently again described from South Georgia 

 by Pfefler under the name Chelonidium, has a iacies with which that of some of the 

 Phliadidai is exactly comparable. Montagu's species has been found in the Medi- 

 terranean, and now a first cousin of it comes to us from Australia. Prom Australia and 

 New^ Zealand together avc ore supplied, as will be sho\\u, Avith four species of this family 

 so remarkably alike in general appearance and in many conspicuous details of structure 

 that one might readily take them for conspecific varieties. Minuter study brings to 

 Ii<'-ht the curious circumstance that thev are not only specitically distinct, but that thev 

 are separated one from another by characters of generic value. 



After one or two notes on the family Melphidippidse, the paper concludes with the 

 definitions of several new genera within the family of the Gammarida?. The genus 

 Gmmnarus may be regarded as antediluvian, because, since its institution by Fabricius 

 in 1775, a whole flood of genera has issued from it. With successive restrictions it still 

 remained unwieldy. The researches of DyboAvsky in Lake Baikal added a hundred and 

 fifteen species within the compass of a single treatise. Some of the Lake Baikal forms 

 differ so strikingly that it requires either a very lax or a very lofty standard of generic 

 value to allow the comprehension of their varied charactei-istics within a single genus. 

 It is useless to apologize for the institution of new genera. Their fate not uncommonly 

 is at first to be abused as needless, inconvenient, and ill-constructed. Attempts are 

 sometimes made to ignore them and set them aside. Then, as time goes on, they are 

 found to be necessary, they are recognized, and pass into circulation as current coin of 

 the scientific realm. 



The redistribution of species of Gammaridai here offered would more naturally, as it 

 seems to me, have appeared in that general account of the Amphipoda which is being- 

 prepared for ' Das Tierreich.' But the organizers of that vast scheme of zoological 

 publication have passed a self-denying ordinance. Novelty is excluded. There are to 

 be no surprises. The contributor is not to expand the sum of knowledge, but to con- 

 dense it. Prom one point of view this is a Avise and considerate arrangement, but it has 

 a drawback. In surveying any large group of the animal kingdom, especially among 



