Sludios on iiiariiie Ostracods 615 



Concfioecia caudata, (I. \V. Mii.i.KU, 1906a, p. 65; pi. XI. fig. 24 and pi. Xll, 



figs. 1—9. 

 dasyophthnlma. ., „ „ 1906 a, p. 66; pi. XI, figs. 20— 23 and 26— 30. 



Is this group a natural one? .( criticism uj this 



As I was only able to investigate closely one of the above-mentioned species it is exceed- group. 



ingly difficult for me to decide this question on account of the incompleteness in the de- 

 scriptions of these forms. It seems to me, however, fairly certain that it must be answered in 

 the negative. 



Both G. W. MUller's characterization of this group and C. Claus's diagnosis of the 

 genus Paraconchoecia are exceedingly incomplete and leave the reader anything but convinced 

 as to the justification of including the species in question in one group. G. W. MUllkh himself 

 states (1906 a, p. 52) that it is not possible to define precisely and characterize this group. — 

 In order still further to explain this fact I shall give here a critical exposition of the characters 

 put forward by these writers. 



Shell: — According to C. Claus this is ,,sehr zart vmd stark comprimiert, meist mit 

 einem Stachelfortsatz am Hinterende der rechten Klappe". G. W. MOller only adopts the 

 last of these characters; according to the latter writer the shell is characterized, in addition, 

 by the fact that the unsymmetrical glands emerge for the most part ,,at the usual place" and 

 by the absence of lateral groups of glands. 



With regard to these characters the following facts may be stated: The species of this 

 group that I investigated, namely C. oblonga, is not characterized by a more thin-walled shell 

 than many other species belonging to other groups of this genus. — The shells of species in this 

 group are not, or at least not essentially, narrower than in most other sjjecies of this genus, — 

 These two characters were, as has been pointed out above, not included by G. W. MiJLLER. — 

 The posterior dorsal corner of the right valve is armed with a more or less well developed spine 

 not only in a rather large number (nineteen) of species belonging to several other groups of this 

 genus but also in representatives of two of the three other genera of this family, namely Archi- 

 conchoecia and EuconcJioecia. In addition, an armature of this kind is, as both C. Glaus and 

 G. W. MUller have pointed out, not characteristic of all the species in the group under consid- 

 eration here ; both C. inermis and C. dorsotuberculata have no spines at all either on the left or the right 

 valve. It is also to be noted that we are here concerned with a character that sometimes varies 

 even within the species, a fact that G. W. MUller himself has observed; cf. this writer's work 

 1906 a, p. 53. — The fact that the unsymmetrical glands have their exits ,,an der gewohnlichen 

 Stelle" is, of course, a character of little value. This character, which is found in most species 

 of the genus Conchoecia, is presumably an original one in this genus, as is shown with a fairly 

 great degree of certainty by the fact that these glands also have this position in the genus Halo- 

 cypris. Moreover these glands have, as G. W. MOller himself has pointed out, been rather 

 considerably displaced in not less than four species of this group, namely C. aequiseta, C. hirsuta, 

 C. dorsotuberculata and C. mamillata. — The absence of lateral groups of glands in these species 

 is certainly also primitive. Such groups of glands are only found in the genus Conchoecia; 

 in all other genera of this sub- family they are always absent. In the geims Coitchoecia there are 



