191 



after the system devised byLovén(1892)in showing Echinoid structures. 

 In this figure the amount of distortion that each area has undergone 

 is more clearly shown than in Fig. I. I have indicated only those 

 sutures that I could determine beyond doubt, and such as remain 

 undetermined are perhaps unimportant. Any further development of 

 the specimen would certainly destroy it. 



According to the division of echinoid abnormalities into four 

 classes which was made by Bateson (1894), this specimen belongs to 

 class 2, characterized by a total or partial disappearance of a definite 

 system of plates which can be named. In the specimen it was impos- 

 sible to determine the relative position of the madreporic body, 

 because of its position in the center of the apical system. It is there- 

 fore not possible to say positively which ambulacral area has been 

 modified, but we may be sure that it is either the right or left anterior 

 system, according to whether the madreporite belonj^s to inter-ambu- 

 lacrum I or V. The eccentric position of the apical system , and its 

 migration away from the anus, the marked bilaterality, and the almost 

 complete reduction of one ambulacral system give the specimen much 

 the appearance of one of the Petalostichous Echinoids. It is extremely 

 improbable that this resemblance has any significance in any phyletic 

 or atavic sense. 



The specimen herein described has been deposited in the Museum 

 of Comparative Zoology at Cambridge, Mass. 



Yellow Springs, O., Jan. 26, 1901. 



Papers Cited. 



1894. Bateson, W., Materials for the study of Variation, New York, London, 

 XV -1-598. p. 441— 447. 



1892. Lovén, S., Echinologica. Bihang till Kongl. Svensk. Vetenskaps-Akad. 

 Handl., B. 18: IV. Stockholm. 



5. Mittheilungen aus der Biologischen Station zu Plön, Holstein. 

 Über einige bisher unbekannte Süfswasserorganismen. 



Von Max Voigt (Plön). 



eingeg. 1. März 1901. 



Bei der im August 1900 begonnenen Bearbeitung der Rotatorien 

 und Gastrotrichen, sowie der Fischparasiten der Plöner Gewässer 

 wurden bis jetzt nachfolgende, bisher unbekannte Süßwasserorganis- 

 men aufgefunden. Eine ausführliche Beschreibung und Abbildungen 

 der neuen Formen beabsichtige ich in dem IX. Forschungsberichte 

 der Plöner Biologischen Station zu geben. 



