studies on marine Ostracods 85 



presumably to be considered as having undergone a secondary simplification — it is of the 

 foliaceous type. Its protopodite, which dominates somewhat over the exopodite, is broad 

 and powerful, in most cases more or less distinctly two- or three-jointed and is closely joined 

 to the body; each of the three protopodite joints is armed on its inner edge with a short but 

 powerful endite. On the outside of the procoxale-coxale part of the protopodite there is an 

 epipodial appendage that is developed into a very large and powerful vibratory plate. The 

 exopodite has in most cases four or five joints; of these joints the two proximal ones are in most 

 cases very strongly chitinized and are each provided on the inner edge with a low, but powerful, 

 endite, armed with powerful bristles and teeth; the following two or three exopodite joints 

 differ in most cases very considerably from the preceding ones in their structure, as they are 

 very slightly chitinized and their bristles are most frequently rather soft and plumous; the 

 end joint has a somewhat varying number of bristles. There is no endopodite on this limb. 

 In the Halocyprids the protopodite of this limb is moderately large and sometimes has two 

 joints; the boundary between these two joints is, however, rather weakly developed; the protopodite 

 is somewhat less closely united to the body than in the preceding family; the basale has only 

 one or two very small endites. On the outside of the procoxale-coxale part of the protopodite 

 there is an epipodial appendage that is developed as a vibratory plate; this is somewhat smaller 

 than in the preceding family. The endopodite is developed as a short, imjointed, powerful 

 masticatory process. The exopodite is elongated and rod-shaped, with three or four joints 

 {Thawnatocypris has four joints, all the other forms only three), its distal joint is small and has 

 three bristles. In the Polycopids the protopodite is very powerful and dominates very 

 strongly over the exopodite and the endopodite; in most cases it is more or less distinctly 

 three-jointed, without endites. On the outside of the procoxale-coxale there is a rather large 

 vibratory plate, the epipodite. The exopodite and endopodite are short, verruciform, un- 

 jointed, the exopodite has a somewhat varying nmnber of distal bristles. In Cypridae, 

 Darwinulidae, Nesideidae and Cytheridae we find a fifth limb that reminds us very much of 

 this appendage in the Halocyprids. The protopodite is imjointed; in most cases it is 

 much more free than in the preceding groups. The endopodite is sometimes developed as a 

 more or less powerful, unjointed, masticatory process; often, however, it is more or less comple- 

 tely reduced. The exopodite is more or less elongated and has at most four joints, e. g. in 

 Macrocypris, often three joints and sometimes two or one; in many forms it has three bristles 

 distally, in others only one or two, but the evidence seems to show that three bristles is the 

 original number for these families. The protopodite sometimes has a fairly well-devoloped epi- 

 podial vibratory plate, but this organ is often more or less completely reduced. Cytherellidae 

 (in the male): The protopodite is unjointed, the endopodite is developed as a rather long, 

 unjointed process for introducing the food into the mouth. The exopodite is elongated, three- 

 jointed; its end joint is small and has only two bristles. The epipodite, the vibratory plate, 

 is well developed and large. 



Which of these types is the most primitive? 



Most investigators of this subject assume that the foliaceous type that we find in the 

 C y p r i d i n i d s is the most primitive. On the other hand G. W. MCl.LEll assumes, as we 



