1900.] FROM THE FALKLAND ISLANDS. 541 



rostral projection, by having no lateral teeth on the margins of the 

 carapace, and by having the subapical appendages of the telsoa 

 smooth, not to speak of the evidently misrepresented mandible. 

 To this it might be reasonably answered that the points in question 

 are such as Claus might easily have overlooked while attending to 

 features that were more striking or that seemed more important. 

 But there is one feature to which both Sars and Claus have 

 evidently paid exceptional attention — the metamorphosed first 

 pleopods of the male. As each author gives a highly magnified 

 drawing of the complicated inner branch of these organs, there is 

 not the least reason to presume inattention or error, and yet the 

 details are so different that, if such details have specific value, 

 these must separate the forms described by Claus and Sars. In 

 that case the E. pellucida of Sars (not Dana) will become Eujyhausia 

 bidentata Sars, since that author had already described it in 1892 

 as Tfiysanopoda bidentata, from the Norwegian coast. 



In 1883 seven species were added to the genus by Sars from the 

 ' Challenger ' gatherings, and three by Ortmann in 1893 from 

 the Plankton Expedition. A new one is now contributed from 

 the Falkland Islands, so that, if all be vahd, there is a total of 

 seventeen species, without reckoning the possibility that the 

 name splende^is may cover two distinct forms. 



Since the keys for specific determination supplied by Sars and 

 Ortmann vi'ill now require to be modified, it may be worth while, 

 uith reference to future as well as to past discoveries, to consider 

 the characters which have been used or which are available for the 

 distinguishing of species in this family. It should, however, be 

 premised that in some instances the stability of a character within 

 any particular species still awaits confirmation, and that characters 

 which in words are the most clear, definite, and convenient are 

 not always equally easy for observation. Tor example, the pro- 

 jecting tooth of the third pleon-segment may be so fine-drawn, so 

 transparent, so closely adpressed to the following segment, as to 

 beguile the observer into believing it to be absent, and the actual 

 absence of so delicate a process might conceivably occur without 

 transcending the limits of individual variation. It would be im- 

 portant also to learn whether the presence or absence, and position 

 when pre sent, of marginal teeth on the carapace can be depended on 

 as specifically constant, and whether the sexual characters of the 

 pleopods in the adult male are trustworthy for specific differenti- 

 ation. Similar questions will readily occur at various points fo 

 the list which follows : — 



1. The size and sluipe of the rostral projection. — The subquadrate 

 form, distally truncate in latifrons Sars, produced to a median 

 spike in schoiti Ortmann, is peculiar to those two species. Ort- 

 mann's species in the pectinate margin of the rostral plate and the 

 postero-dorsal spike of the carapace uniquely retains two larval 

 characters. In all the other species the rostral projection is more 

 or less triangular, though varying much in length, breadth, and 

 acuteness of the apex. Dana says of E. superba, " carapace with a 

 very short and acute beak ;" whereas Sars says, " rostral projection 



Proc. Zool. Soc— 1900, No. XXXVI. 36 



[25] 



