Petalostoma minutuni Kefeestein. 37 



satzstellen der Eetractoren hat Théel wieder eingehendere Unter- 

 suchungen angestellt, die zum Resultat geführt haben, daß Zahl 

 und Lage der Retractoren nicht unbedingt als Merkmale zur Unter- 

 scheidung der Arten benutzt werden dürfen. Ich lasse deshalb hier 

 seine Ausführungen folgen: „If we now pass on to the retractor- 

 muscles and their points of attachment, it becomes evident that here 

 too no true species characters can be given ... In order to adduce 

 proof of my statement that the retractors are of but questionable value 

 for the systematic arrangement of the species in question, I refer 

 to the annexed table, which represents an excerpt of ray annotations 

 upon more than 200 individuals of Ph. sabellariae and improvisuni, 

 which I have had the opportunity of invei^tigating . . .•' Es folgt 

 die Tabelle. Dann sagt er weiter: „From the table above it is evi- 

 dent that the length of the retractors, their attachment to the 

 body wall, and the degree of their coalescence are subject to rather 

 considerable variations. This is strikingly obvious in Ph. improvisuni, 

 where the differences between the extreme forms are so enormous, 

 that they doubtless should be considered as distinct species, did they 

 not present series of transitional stages and did they not, besides, 

 live together, side by side, on the same shells and between the 

 same sandy tubes of Sahellaria. Considering this, it lies very near 

 to hand to assume that such a variation is also shown in other 

 forms of Gephyrea and, consequently, that several species have been 

 described as new, which in reality are nothing but varieties of 

 already known ones . . . With special regard to the extent of the 

 coalescence of the two retractors, there seems to exist great differences 

 in the same species. In Ph. improvisuni the retractors have sometimes 

 almost completely grown together, so as to form seemingly a single 

 retractor, embracing the nervous cord with two very diminutive 

 roots." 



Nach meinen Beobachtungen an Ph. minutum waren hier die 

 beiden Retractoren meist ganz frei bis zur Rüsselspitze, jedoch be- 

 obachtete ich auch vereinzelte Fälle, in denen eine kurze Verwach- 

 sung der Retractoren vorhanden war. Für Pli. sabellariae gibt Théel 

 an, daß stets eine Verwachsung vorhanden sei. daß sogar die Länge 

 des verwachsenen Abschnitts die des freien Verlaufes übertreffe. 

 Letzteres ist bei einem von mir geschnittenen Exemplar nicht der 

 Fall; die Verwachsung betrug nur ^'5 der Gesamtlänge der Retrac- 

 toren, und zwar war das mittlere Fünftel verwachsen. Das Ver- 

 halten der Retractoren in diesem Exemplar war ganz überein stim- 



