48 



The genital area (fig. 14) has a somewhat small, rounded tubercle behind the produced 

 posterior corner of each coxa; the furrow between the penultimate and the last thoracic segment 

 is, excepting near the sides, extremely curved with the concavity turning forwards, and the area 

 between this concave furrow and the tubercles mentioned is raised as two large and proportion- 

 ately high, a little oblong, rounded knots separated by a deep median impression. 



Length 2 i mm. 



Remarks. — A. paraguayensis differs from all species described in this paper in 

 having the exopod of the uropods considerably broader in proportion to its length, and in 

 possessing a process on the lower surface of the coxae of third pair of legs, while in other 

 forms a process or tooth, when it exists, projects from the distal inner corner of the coxae. The 

 shape of the exopod of the uropods excludes the possibility that this species could be identical 

 with A. americanus OrXxsx. — Most of the specimens are small and decidedly immature; some 

 among the females are certainly adult; as to the males I believe that some few specimens are 

 adult, but as the curious petasma is without hooks, acute processes or spines on pars media, 

 I am not absolutely certain. 



It is interesting that this species has been taken in a tributary to Rio de la Plata more 

 than a hundred geographical miles from the Atlantic. 



II. Sub-Family Luciferin.e. , 



Lucifer Thomps. 



With good reason the genus Liicifer J. Vaughan Thompson — or Lciicifcr H. INIilne- 

 Edw. — has been separated from the other genera of Sergestidae and established as type for 

 a sub-family. The general morphology is on the whole well known. In 1882 Brooks elucidated 

 the metamorphosis of an Atlantic species, L. Faxonii Borrad., and the material of larval stages 

 secured by the "Siboga" is so small that I leave this topic out of consideration. But the 

 "Siboga" gathered enormous quantities of subadult and adult specimens, in reality a quite unique 

 collection. To separate and name the species with the assistance of the existing literature was 

 found to be impossible, and the result is that I was forced to work out a kind of monograph. 

 The zoological Museum in Copenhagen possesses a good collection of this genus ; the majority 

 of the specimens was taken at a large number of localities in the trojjical and the warmer 

 temperate areas of the Atlantic, but besides specimens are to hand from Aden, the Bay of 

 Bengal, various other places in the Indian Ocean and finally from the Bay of Yeddo, Japan. 

 Consequently I think to possess specimens of every species inhabiting the Atlantic and the 

 tropical seas south of Asia, but unfortunately I have almost no material from the Pacific 

 excepting the areas from southern Japan to the Philippines, and it may be possible that the 

 vast Pacific contains a single or two hitherto unknown forms. 



Before mentioning the literature and the specific characters it may be stated that I have 

 separated six species; even of the most rare of these form I have seen a good number of 



