studies on marine Ostracods 1118 



should not be given too much importance. With regard to the value of the former character 

 the following facts may be instructive. In Thaumatocypris the first antenna is situated 

 somewhat deeper down than in other Halocypriformes. In Cypriformes we find forms 

 with both high and low places of attachment; this antenna of the Cyprids is fixed ,,hoch 

 oben an der Stirn" (G. W. MlIller), while in the C y t h e r i d s and N e s i d e i d s it shows 

 a resemblance to that of the C y p r i d i n i d s „besonders in der tiefen Einlenkung an der 

 Stirn" (G. W. MtJLLER, 1894, p. 29). With regard to the way in which the sexual organs 

 open, we may, in the first place, mention the important differences that are actually 

 to be observed between P o 1 y c o p i d s and Halocyprids, and, secondly, that 

 the Cytherellids are also characterized by an unsymmetrical exit of these organs 

 (Note too the resemblance — superficial, it is true — that exists between the copulation organ 

 in Cytherellids and Halocyprids). I do not think G. W. Mt'LLER would bring 

 forward this character as a sign of close relationship between Cytherellids and Halo- 

 cyprids. In my opinion it is not at all impossible that we have here a phenomenon of 

 convergence. 



Halocypriformes. Cypridiniformes and Polycopiformes are probably to be regarded 

 as three groups fairly independent of each other. That nevertheless they resemble each other 

 not inconsiderably in a number of characters is due, first, to the fact that in several respects 

 they show primiti\e featurs, and, secondly, to convergence. 



It seems difficult to decide which of these three groups is to be taken as the most 

 primitive. The facts of the matter are probably that each group is in a number of respects 

 more primitive than the two others, while in other respects, on the contrarv, it is more 

 developed. Thus, for instance, Cypridiniformes are presumably primitive inasmuch as, let us 

 say, the lateral eyes, median eye, the heart and the two posterior limbs are developed, but they 

 difier from the original type in having a rostral incisur and a rod-shaped organ, and in the 

 structure of the second antenna and the maxilla. Polycopiformes, which have no lateral eyes, 

 median eye, heart or two posterior limbs are, on the other hand, presumably primitive with 

 regard to the rostral incisur, the rod-shaped organ and the structure of the second antenna 

 and maxilla. 



It is at least equally difficult, perhaps even more so, to determine with certainty the Cythereinformes. 

 natural position of the Cytherelliformes in the Ostracod system. 



G. W. MOller placed this group together with the families Cypridae, Darmnididae, 

 Nesideidae and Cytheridae. The same author points out in his work of 1894, p. 190, that the 

 Cytherellids show ,,wenige, aber immerhin beachtenswerthe Beziehungen zu den 

 C y p r i d e n". The characters by which this group would show agreement with Cypriforme,s 

 are the following: Second antenna: The group of sensory bristles on the first joint of the 

 endopodite and the group of five bristles distally on the inside of the same joint. The use of 

 the fifth limb as a clasping organ in the males. 



^V^lat value can we assign to these characters from a classificatory point of view? 



Second antenna: With regard to the second antenna it ought to be pointed out 

 that similar sensory bristles are also found in the Cytherellids proximo-posteriorly on 



