Sliidii'S on riiariiic Ostracods 71 



Ct. W. MilLLFJR seems to liave suspected the weakness of this assumption hiifiself, as he writes 

 ,,vermuthlich" before it. In dealing with this problem the following facts ought to be noted; 

 There are only two groups among the recent Ostracods, namely the C y p r i d i n i d s 

 and the Halocyprids, which are characterized by having a rostral incisur. The 

 C y p r i d s, Da r w i n u 1 i d s, N e s i d e i d s, C y t h e r i d s, C y t h e r e 1 1 i d s and 

 P o 1 y c o p i d s of which the latter group is considered, presumably correctly, to be rather 

 primitive in many respects, and Thaumatocypris , presumably the most primitive genus among 

 the H a 1 o c y p r i d s, have not this peculiarity in their organization. The rostral incisur 

 in the C y p r i d i n i d s is presumably not homologous with that of the Halocyprids. 

 In the Halocyprids the rostral incisur has been partly formed by the outer lamella of 

 the shell having been bulged out like a finger of a glove into a sort of rostrum near the dorsal 

 boundary of the anterior margin of the shell; the margin of the shell continues, as U. W. MOLler 

 himself pointed out in his monograph of 1894, p. 101, in the form of an s-shaped bent line, 

 ,,Buchtlinie" (C. Claus), situated basally on the inside of the rostrum. In the C y p r i d i n i d s, 

 on the other hand, the incisur is formed simply by a concavity of the anterior margin of the 

 shell. In the face of these facts and as there seem to be no reasons to support G. W. MUller's 

 assumption, it does not seem too bold to draw the conclusion that the rostral incisur 

 is not a character which belonged to the Protostracods.* 



Whe thus see the failure of the strongest — and as far as I can see the only — argument 

 in favour of assuming that the Protostracods had a method of swimming of the 

 same type as that of the recent Cy p r i d i n i d s. There is, in addition, at least one more 

 reason that seems to contradict this assumption. G. W. MlJLLER assumed that the second 

 antenna of the Protostracods had both the exopodite and the endopodite well 

 developed and that both these branches were used in swimming (cf. G. W. MUller, 1894, p. 199); 

 this antenna seems to resemble most closely the recent P o 1 y c o p i d s. The assumption that 

 the second antenna originally had both the exopodite and t he endopodite well developed seems 

 to me justified; there are several arguments in favour of this. First, the exopodite dominates 

 in a number of forms (C y p r i d i n i d s and most of the Halocyprids), while the endo- 

 podite dominates in others (C y p r i d s, D a r w i n u 1 i d s, N e s i d e i d s and Cythe- 

 r i d s), secondly, a number of forms, Thaumatocypris, Poly cop ids and C y t h e r e 1- 

 1 i d s, have a second antenna with both the exopodite and the endopodite well developed. 

 On the other hand it seems to be very unlikely that the two branches took part in swimming, 

 at least if we assume the same method of swinmiing for the Protostracods as 



• In this fonncrlion I nuglll perhaps lo nn'iilidn tlic .statrnuMit put fdrwaicj hy C. Clais, 1876. p. 'J, In Ihc 

 (effect thai the deep concavities found behind the ..ear-shaped lobes" anteriorly on the shells of larvae of the Dithelopod 

 genus Euphausia are recurrences of the rostral incisurs in C y p r i d i n i d s and Halocyprids and are of great 

 value phylogenetically. This author writes as follows on this point: ,,Von Interesse scheint mir das Vorhandensein zweier 

 ohrfiirmiger Lappcn an deni als Kragcn bezeichneten Abschnitt der Panzerduplicatur. Eine tiefe Einbuchtung, 

 hinler jedem der beiden Seitenlappen ist eine Wiederholung des Ausschnitles an der Schale der Cypridinen und 

 H a 1 o c y p r i d e n. und waist mit vielem andcren darauf hin, daB wir den Alalacostrakenpan/.er und die Schalen- 

 bildungen der E n I o ni o s t r a k e n von gleichem Ausgangspunkt abzuleiten haben." I give this statement for what 

 it is worth. I ought perhaps to mention, however, the great variation shown in the shape of the shells of larvae belonging 

 to Malacofirnra. Why should just the peculiar type of shell in this genus be of great phylogenelir value? 



