-20 Edward T. Browne. [No. 4 



■attempt ttiis without the aid of sufiicient specimens. For the pre- 

 sent I shall confine myself to two of the genera, Aequorea and 

 Polycanna. 



The genus Aequorea was founded by Péeon (1809) and con- 

 tains the type species, Medusa aequorea of Fobskål (1775). 



Polycanna is a genus introduced by Haeckel (1879) to aid 

 in the further splitting up of the Aequoridae. The chief distinction 

 aceording to Haeckel between these two genera is in the shape 

 of the stomach and the mouth. Aequorea has the stomach short 

 and the mouth wide open.. Polycanna has a funnel-shaped stomach 

 which is capable of twisting and so closing the mouth. The spe- 

 cimens in my collection clearly show that the shape of the stomach 

 and the condition of the mouth depend upon the age of the specimen, 

 the condition in which the specimen was caught, and the method 

 of preservation. The early and intermediate stages have a short 

 stomach, and the mouth is usually more or less open. The large 

 funnel-shaped stomach only occurs in the large specimens and is 

 a sign that the medusa has reached its adult growth. The funnel- 

 shaped stomach is not a permanent feature, because directly the 

 medusa opens its mouth the stomach becomes like an open bag with 

 a circular mouth. It is in this last condition that some of the larger 

 species of the genas Aquorea have been described and figured. 



The Norwegian specimen has not got its stomach spirally twi- 

 *sted and its mouth is nearly closed, the wall of the stomach only 

 being slightly contracted back. It has the characters of the genus 

 Aequorea, but probably when it was aiive it could twist its sto- 

 mach and become a Polycanna. 



My small collection of British Aequoridae being in a state of 

 confusion, after several attempts to determine the species, I had 

 little hope of succeeding with the Norwegian specimen. I made, 

 however, another examination of all the specimens with the hope 

 of iinding a character which is constant at all stages in the devel- 

 opment of a species, but differs among the species. I selected the 

 shape and the size of the basal bulbs of the tentacles and made a 

 series of drawings on the same scale. By the aid of the basal 

 bulbs I am able now to group my specimens, showing different 

 stages in development, into three sets, which with other characters 

 show three well marked species. 



The basal bulbs of Aequorea (Polycanna) forskalea, Fokbes, are 

 •quite different from those of Aequorea (Polycanna) vitrina, Gosse; 



