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Show 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 telson 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 Euphausia bidentata Sars, since that author had already described it in 1892 as Thysanopoda 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 Planktou Expedition. A new one is now contributed from the Falkland Islands, so that, if all be valid, there is a total of seventeen species, without reckoning the possibility that the name splendens may cover two distinct forms. Since the keys for specific determination supplied by Sars and Ortmann will now require to be modified, it may be worth while, with 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. For example, the projecting 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 important also to learn whether the presence or absence, and position when pn sent, of marginal teeth on the carapace can be depended on as specifically constaut, and whether the sexual characters of the pleopods in the adult male are trustworthy for specific differentiation. Similar questions will readily occur at various points fo the list which follows :- 1. The size and shape of the rostral projection.-The subquadrate form, distally truncate iu latifrons Sars, produced to a median spike in schotti 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 |