PTYCHOGENA ERYTHROGONON. 151 



addition to the well-developed tentacles several specimens have one or two 

 small ones, evidently in process of development (PI. 39, fig. 5). The ten- 

 tacles are very short and stout; their conical basal bulbs (PI. 39, fig. 5) are 

 not laterally compressed as they are in P. lactea and P. antarctica, but more 

 nearly resemble in outline the corresponding structures as they are described 

 in the various species of Laodice. This difference in the form of the basal 

 bulbs in different species of the genus is probably correlated with difference 

 in the number of tentacles ; the bulbs are laterally compressed in species 

 in which the tentacles are crowded, and conical when these organs are 

 widely spaced. 



Cirri — In addition to the tentacles there are a small number of solid cirri 

 (PI. 39, fig. 5), which bear nematocyst clusters at their tips (PI. 38, fig. 9). 

 In none of the specimens did I find more than three of these structures ; 

 several had only one or two, and others had none at all. 



Cordon. — These organs (PI. 39, fig. 5, co ; PI. 38, fig. 8) are of the struc- 

 ture so well described by Brooks ('95) for Laodice. They contain no oto- 

 lithic concretions of any kind. As a rule there is one cordylus between 

 every two tentacles ; but occasionally there are two, so that in every indi- 

 vidual in which they were counted the number of cordyli slightly exceeds 

 that of tentacles (PI. 39, fig. 5). It is evident, then, that the question whether 

 there are one or two between every two tentacles is of no greater systematic 

 importance in Ptychogena than Browne (: 07) considers it in Laodice. 



Manuhrimn. — The manubrium is quadrate basally ; in young specimens it 

 is very large (PI. 39, fig. 6), but its growth does not keep pace with that of 

 the bell, so that in adults it is proportionately much smaller. It is barrel- 

 shaped in outline, and the mouth is surrounded by a simple circular thicken- 

 ing, widely open in all the specimens (PI. 39, fig. 7). In oral view it much 

 resembles the figure given by Maas ('93, taf. 6, fig. 7) for P. longigoim, as 

 well as for Laodice fijiana (Maas, : 05, taf. 5, fig. 5^). 



Radial canals and gonads. — In the smallest specimen the radial canals, 

 though broad, are simple in outline, without diverticula or even waviness 

 (PL 39, fig. 6) ; but in the specimen 24 mm. in diameter they have developed 

 a series of short lateral diverticula along the narrow lines by which they 

 are attached to the subumbrella (PI. 39, fig. 2). The main bodies of the 

 canals, however, are so stout that they extend out as far as the ends of these 

 short branches. The gonads develop in the spaces between the diverticula, 

 and are confined to the aboral surfaces of the canals, close to the subumbrella. 



