— 4 — 



nopoda elongata Guer. must be cancelled, as the descrip- 

 tion (with figures) is quite insufficient for the recognition 

 of the species, and the type has disappeared. I thought it 

 useful to write this treatise, as a few years may elapse 

 before all reports on the collections to hand can be pub- 

 lished, and as several Zoologists are occupied with the 

 study of material of this order. 



Finally the chapter on variation. While writing this 

 paper I was forced to examine more closely Rhoda iner- 

 mis Kr. and Thysanoëssa neglecta Kr., as at least three 

 times since 1 885 I had met with difficulties in referring 

 several specimens to either of these species. And the result 

 of the new investigation was somewhat startling, showing 

 a variation of a quite unusual quality. Consequently 

 I deemed it practical to deal with this topic in a separate 

 chapter, and to add a short account of some other cases 

 of interesting variation, omitting all differences arising 

 from age, sex or pure anomalies. And I write this chapter 

 in the hope that it may be of some interest to several 

 Zoologists besides those occupied with an investigation of 

 animals of this order. 



II. REMARKABLE VARIATION. 



A. Variation in Carapace or Abdomen. 



i. In 1894 Ortmann established Euphansia diomedeœ 

 on a couple of specimens from the Pacific possessing a 

 peculiar character, viz. a quite extraordinary expansion 

 of the frontal plate « arched over the eyes, and covering 

 their peduncles », while the rostral process is very short. 

 As already mentioned in the « Siboga » report, I have a 

 large material from the Indian Archipelago and a very 

 large number of specimens from the East Pacific of this 

 species, but all specimens from the Dutch India and 

 most from the Pacific have the frontal plate not covering 



