PTYCHOGENA. 149 



mouth, and ocelli on the basal bulbs of the tentacles ; Staurophora, differ- 

 ing from Laodice by the peculiar and extensive development of the mouth ; 

 Ptychogena, resembling Laodice except in lacking ocelli ; Saurodiscus, in 

 which each of the four radial canals has two lateral branches ; Toxorchis, 

 with six branched radial canals; and Melicertissa with eight unbranched 

 canals. The present collection contains examples of one only of these 

 genera, Ptychogena. 



Ptychogena A. Agassiz, 1865. 



sens. em. Browne (: 07). 



Laodiceidae with four unbranched radial canals ; with central mouth and 

 stomach ; without ocelli on the basal bulbs of any of the tentacles. 



According to Browne's revision of this genus three species can be recog- 

 nized : — P. lactea A. Agassiz ('65), P. hngigona Maas ('93), and P. antarctica 

 Browne (:02), of which otdy a preliminary account has yet appeared. P. 

 pinnulaia Haeckel ('79, '81) appears to be indistinguishable from P. lactea, 

 since the slight differences in the form of the gonads supposed by Haeckel 

 to separate the two species represent nothing more than different stages 

 in development. Indeed an intermediate step between the two has been 

 described by Linko (: 00). As Browne says (: 07, p. 473), P. lactea is prob- 

 ably an arctic species, and there is no evidence that it belongs to the inter- 

 mediate fauna. P. lonc/ic/ona is distinguishable from P. lactea by the length 

 of the gonads, which extend along the entire course of the radial canals, 

 and by the fact that there are no distinct lateral diverticula on the radial 

 canals, although the gonads are arranged in folds. Unfortunately the margin 

 has not been figured, so that I can say nothing as to the form of the basal 

 bulbs of the tentacles, a feature which appears to be of some systemic sig- 

 nificance in this genus. In P. antarctica, founded for a single fragmentary 

 specimen, the radial canals have wavy margins corresponding to the principal 

 folds of the gonads; but no true diverticula such as are seen in P. lactea 

 (Browne, : 07, p. 474), and the red color of the tentacles of P. antarctica 

 further serves to separate the two; the tentacular bases, however, like those 

 of P. lactea, are laterally compressed. From P. lunaigona it is apparently 

 distinguishable by the shortness of the gonads; but Browne (: 07) states 

 that, owing to the brevity of Maas's description of the latter, the relation- 

 ship of the two is doubtful. For a final decision on this point we must 

 await the full description and figures of P. antarctica. 



