studies on marine Ostracods 73 



G. W. MOller has done. On the contrary, the facts of the case will probably make us admit 

 that it is still impossible to express our opinions with any great degree of certainty on this 

 important problem, that of the mode of locomotion of the Protostracods. 



Shell: — G. W. MOller's assumption that the Protostracods had a calci- ■S''^"- 



fied shell, enclosing the whole body, and that it was shut by a muscle that went through 

 the body, is probably correct. At least it seems to be supported by the fact that almost 

 all the recent Ostracods so far known are distinguished by a shell of this sort.. 

 With regard to the assumption that the shell was characterized by a rostral incisur I shall 

 only refer here to what has been said on this matter above, p. 71. It seems at present to 

 be impossible to decide as to the correctness of the assumption that the shell had an arched 

 ventral margin, which was gradually flattened in a number of forms „entsprechend der krie- 

 chenden Lebensweise". G. W. MtJLLER has not produced any reason for this assumption 

 and I cannot find any definite reason either for or against it. We can find shells with a 

 flattened ventral margin both in swimming and in crawling forms. But the arched ventral 

 margin predominates in the swimming forms, the flattened one in the crawling forms. Presumably 

 the dorsal margin had no hinge teeth. 



Segmentation: — As is seen above, the body would have been segmented externallv; Segmemaiion. 

 at least eleven segments would have been developed behind the head, only a number of which 

 had limbs. 



In the same work, p. 18, G. W. MULLER points out that the recent Ostracods 

 almost always lack external segmentation of the back of the body. Only in a single one of the 

 genera investigated by him, the genus Cytherella, did this segmentation seem to exist. He 

 writes as follows about this: ,,Nur Cytherella hat zu beiden Seiten der hinteren Korperhalfte 

 eine Reihe von gelenkig verbundenen Chitinstiicken. Diese stehen in keiner directen Beziehung 

 zu den GliedmaaBen, wie etwa die Chitinstiitzen der Cytheriden, das beweist schon ihre 

 Zahl. Vielmehr haben wir in ihnen unzweifolhaft Reste einer Segmentirung zu sehen. Von 

 den GliedmaaBen bei den Weibchen von Cytherella gehort das einzige wohl entwickelte des 

 Thorax, das wir als 4. postorales deuten, deni zweiten Segment an, dann ware das 3. postorale 

 auf den 1. gesonderten Ring zu beziehen. Es wiirden dann fiir den unsegmentirten Kopf 4 Glied- 

 maBen bleiben, die gleiche Zahl, die wir oben angaben. GliedmaaBen lassen sich am Thorax der 

 Ostracoden mit einiger Sicherheit 4 Paar nachweisen (auBer den bekannten GliedmaaBen 

 betrachte ich als GliedmaaBenrest das biirstenformige Organ). Es wiirden dann beim Weibchen 

 von Cytherella noch 7 Segmente ohne Extremitiiten bleiben." A reference is given in the 

 text to pi. 32, fig. 12, Cytherella sordida, G. A\'. MCller, $. As far as I can discover, 

 G. W. MtlLLER rests his assumption about the segmentation of the Protostracods exclusiv- 

 ely on this genus, on a single species, or, more correctly speaking, on the female of a single 

 species, C. sordida, of this genus. He has even only paid attention to the chitinous stripes he 

 found on the back of the body in this form. 



Unfortunately I have not had any opportunity myself of investigating closely any repre- 

 sentative of this genus. In discussing this problem I was consequently confined to the 

 description and figures given by G. W. MtJLLER. 



Zoolog. bidrag, Uppsala. Suppl.-Bd. I. 10 



