398 PROCEEDINGS OF UNITP]D STATES NATIONAL MUSEUM. [1885. 



Family STOMOLOPHID^. 



Stomolophus meleagris, Agassiz. 



Specimen examined. 



Family CASSIOPBID^. 

 Oassiopea frondosa, Lamarck. 



Specimen examined. 



The teratology of the medusan group from many considerations is a large 

 field for research. We have all kinds of variations in organs, their ar- 

 rangement, number, bifurcations, modes of development, and the like. 

 The genus Oassiopea seems particularly subject to such abnormalities 

 as its mode of life and anatomy might suggest. I have already de- 

 scribed in Oassiopea {Bull. Mus. Oomp. Zool., vol. ix, No. 7) variations 

 in the number of marginal sense bodies, and the existence of two ocelli 

 on one " sense club," and two otocysts on the same peduncle. The ab- 

 normal condition described below is one which I have never before met 

 with. The irregularity consists in the addition of a new oral arm on 

 the under oral side of the subumbrella, homologous with one of the 

 branching organs from the oral cylinder, although not arising from that 

 body. 



The oral cylinder appears to be normal on the under side of the 

 umbrella, about one-half the distance from the edge of the base of the 

 same to the bell margin, in the same radius as one of the normal oral 

 arms adjoining that in which a sexual opening lies, there is an addi- 

 tional rudimental oral arm. This structure resembles the distal ex- 

 tremity of a normal arm and arises by a gelatinous base from the under 

 surface of the bell walls. It is gelatinous, bifid, with sucker-frills along 

 its free edge as in normal rhizostomatous genera. 



The line of junction with the lower surface of the umbrella is at right 

 angles to the radius in which it lies. It is separated from the oral cyl- 

 inder by an unmodified, normal, region of the umbrella. 



I have not dissected its attachments and therefore am unable, to speak 

 of modifications of chymiferous tubes, if such occur in the immediate 



