20 



MNEMIOPSIS LEIDYI. 



Mnemiopsis Gardeni Agass. 



Mnemiopsis Gardeni Agass. Cont. Nat. Hist. U. S., m. pp. 269, 290, Figs. 95, 96. 1860. 



The accompanying figures (Figs. 20, 21) of 

 3Inemio2)sis Gardeni Agass. are here introduced 

 to show how striking are the differences in the 

 proportions of the two Medusse of this genus 

 found upon our coast. The great length of the 

 digestive cavity, together with the size of the 

 aui'icles and lobes, enable us at once to distin- 

 guish this species from its ally, the Ilnemiojisis 

 Leidyi A. Agass. The genus Mnemiopsis had 

 been placed by Professor Agassiz among the 

 Mnemiidge, on account of the deep furrow sepa- 

 ratmg the anterior and posterior lobes from the 

 lateral spheromeres. The differences of form 

 based upon this structural feature, which are in 

 such striking contrast in Bolina and Il^iemiojisis Gardeni, are far from 

 being marked when we compare Bolina alata and 3Inem,iopsis Leidyi. 

 Charleston, S. C. (L. Agassiz). 



Mnemiopsis Leidyi A. Agass. 



This Medusa would readily be mistaken for a true Bolina, at first 

 glance ; a closer examination, however, will show that, notwithstanding 

 the short digestive cavity which reminds us of Bolina, we have the 

 deep furrow separating the anterior and posterior lobes from the lateral 

 spheromeres. The long ambulacra are covered with locomotive flap- 

 pers to the actinal margin, and we have long auricles, showing that 

 this is a Mnemiopsis, with longer anterior and posterior lobes than we 

 have in the llnemiojjsis Gardeni Agass. 



This species grows very large, specimens measuring six and even 

 eight inches in length are frequently found. Like the other Cteno- 

 phorte of our coast, it is gregarious ; thousands being collected to- 

 gether basking in the sun. It is exceedingly jjhosphorescent ; and 

 when passing through shoals of these Medusae, varying in size from 

 a pin's head to several inches in length, the whole water becomes 

 so brUhantly luminous that an oar dipped in the water up to the 



Fig. 20. Mnemiopsis Gardeni seen from the broad side, a, folds of digestive cavity. Letter- 

 ing of Figs. 20 and 21 same as Fig. 19. 



Fig. 21. Fig. 20 seen from the actinal pole, o, mouth ; l\ l\ lateral ambulacra ; /, x\ auri- 

 cles ; 1°, l^, I', 1% anterior and posterior ambulacra. 



