PORPEMA PRUNELLA. 325 



The relationship of P. globosa to the Pacific P. prunella can not be deter- 

 mined from the accounts yet pubhshed, because Haeckel studied only young 

 stages of the latter. Fortunately, however, the present collection contains a 

 large and excellently preserved series of adults, which differ from P. prunella 

 only in such features, i. e., greater number of gonozooids and tentacles, as are 

 undoubtedly due to a more advanced stage in growth, and which must therefore 

 be referred to that species, as indeed we would expect from the locality of capture. 

 A comparison between them and Haeckel's account and figures of P. globosa 

 ("P. medusa"), shows that it is doubtful whether any specific demarcation can 

 be drawn between the Atlantic and Pacific forms. Such minor differences as do 

 exist in form, number, and size of tentacles are readily explained as due to slightly 

 different stages in growth and to different methods of preservation. But 

 Haeckel's account is too general and his figures too diagrammatic to allow of a 

 certain conclusion. And since I have no Atlantic specimens at hand, it is better 

 to follow the more conservative course of retaining prunella and globosa as two 

 separate species, at least until Atlantic material can be restudied. 



Judging from the localities of capture it is probable that P. lenticula Haeckel, 

 from the Indian Ocean, and P. pileata Haeckel from Chile are both in reality P. 

 prunella; but in the absence of any description, we can not be certain of this. 

 They must be treated as nomena nuda, since a mere geographic location can not 

 be considered as "indication" in the nomenclatural sense. 



Discalia medusina Haeckel is the young of some Porpitid; the compara- 

 tively great thickness of its disc suggests that it belongs to Porpema, and its 

 locality, South Pacific, points to identity with P. prunella. 



Porpema prunella (Haeckel). 

 Plate 25, 26, 27; Plate 28, fig. 11, 15. 



Porpalia prunella Haeckel, '88a, p. 30; '88b, p. 58, pi. 48. 



? Discalia medusina Haeckel, '88a, p. 20; '88b, p. 46, pi. 49, fig. 1-6. 



Porpila globosa Schneider, '98, p. 195 (part ini). 



Station 4685 surface 37 specimens, 5-6 mm. in diameter, preserved in 



formalin, in alcohol, in corrosive acetic, and in 



Flemming's fluid. 



" 4686 " 4 specimens, 6 mm. in diameter. 



The general structure of a young stage of this species has been described 



and figured by Haeckel in some detail. The present adult specimens differ 



from his account in the various characters which change with growth, while 



