330 Dr. F. Cohn on a new genus of the family 0/ Volvocinese. 



Gonium and Pandorina, and the organism here described; and 

 these genera are only essentially distinguished by the arrange- 

 ment of the green globes or primordial-cells, which in Pandorina 

 are placed on a spherical sm-face, in Gonium on a flat plane, while 

 in our form they stand at the circumference of a circle. Since, 

 however, this very law of arrangement is, in the family of the 

 Volvocinece, the most important criterion, on which the establish- 

 ment of the genera depends, it follows, that we here have a pe- 

 culiar genus, which I do not find described either in Ehrenberg's 

 great work or in any later publication. 



I owe to the friendly information of Major von Flotow the 

 only notice which can perhaps refer to our form. 



In the Berlin ' Haude-Spener's Zeitung ' of the 28th of April 

 1846, namely, occurs the abstract of a paper read by Ehrenberg 

 on April 24th before the Society of '' Naturforsch. Freunde.'' 

 This states that " in this spring he had observed a new generic 

 form of the naked animalcules of the Berlin district, which was 

 closely allied to the green plate -animalcule composed of sixteen 

 corpuscles, called Gonium pector ale. Herr Werneck had already 

 discovered an allied new form near Salzburg, which was not 

 tabular but spherical, and formed of eight animalcules, and this 

 he called Stephanoma. The new form consisted of 6-21 annu- 

 larly connected animalcules, was tabular, and each of the cor- 

 puscles appeared to bear two proboscides or locomotive organs, 

 with which it moved actively like a rolling wheel. It was de- 

 nominated Trochogonium Rotula." 



So far as can be made out from this, unfortunately very im- 

 perfect and obscure statement, regarding which I could nowhere 

 find any more minute details, the two genera, Trochogonium, Ehr., 

 and Stephanoma, Werneck, are the only ones which admit of 

 being placed in a parallel with our form. At the same time, 

 Ehrenberg's Trochogonium cannot possibly be identical with the 

 latter, since this is said to be composed of 6-21 globes, while the 

 structure described here is never formed of more than eight 

 green primordial-cells : moreover Ehrenberg says nothing of a 

 spherical envelope ; from the statement that its form is tabular 

 and nearest allied to the genus Gonium, it seems rather to fol- 

 low, that a flat envelope exists in Trochogonium. 



On the other hand, a greater agreement is exhibited by Wer- 

 neck's genus Stephanoma, which Ehrenbei'g himself mentions as 

 a form generically different from his ; and I should not hesitate 

 to call my organism identical with Werneck's, if reasonable doubt 

 were not excited by the expression of Ehrenberg, that the latter 

 is composed of eight, not tabularly, but spherically combined 

 animalcules. For in the above description no distinction is 

 made between the shape of the envelope and the figure formed 



