Chap. I. SUB-ORDERS OF THE DISCOPIIOR^. 



SECTION II. 



SUB-ORDERS OF THE DISCOPHOR^ PROPER. 



Having pointed out the typical differences which distinguish the Discophoroe 

 Cryptocarpse and the PhanerocarpjB, I feel justified in maintaining that these two 

 groups of Acalephs ought to be considered as belonging to different orders of their 

 class; and that, while the Phanerocarpte constitute an order by themselves, for which 

 I retain the name of Discophorae, the Cryptocarpas must be united with the Siphon- 

 ophorse and the Hydroids proper, with which they agree much more closely in 

 their structure than with the PhanerocarpjB. There can be no doubt that the 

 Discophoroe proper are superior to the Hydroidaj and Siphonophorte, and Eschscholtz 

 has already pointed out their affinity to the Ctenophorae, arising from the fact 

 that their body has generally eight prominent segments; that is to say, the Dis- 

 cophoriB, like the Ctenophorse, are built of eight spheromeres, while the Hydroidte 

 generally number only four. 



We have now to consider the natural subdivisions of the Discophorte proper. 

 Thus far, the many and most diversified representatives of this beautiful order of 

 Acalephs have generally been divided into two families only, the Medusidae and the 

 Rhizostomidae, first characterized by Eschscholtz ; or, when further subdivisions have 

 been proposed, as was done by Tilesius, Brandt, Les,son, and Gegenbaur, these were 

 also considered as families, the characters upon which the new groups were founded 

 being of the same kind as those adduced by Eschscholtz. But while I believe 

 with Gegenbaur, that the Acraspeda (Discophorce proper) include a larger number 

 of families than were admitted by Eschscholtz, I am further satisfied that this order 

 contains not only well-marked fiimilies, but also several structural types of a higher 

 rank than that to which natural families are entitled. 



Assuming for the present, that the groups of DiscophorJB called by Tilesius, 

 Rhizostomete, Cephete, and Cassiopeae, are natural families; that those he has desig- 

 nated as Pelagiaa and Aurelise are also natural families ; and that to these the Cyaneae 

 and CharybdeiB must also be added as natural families, the natural limits of which 

 we shall consider hereafter, — it should not be overlooked that the RhizostomeJB, the 

 Cepheae, and the Cassiopeae have certain characters in common which separate them 

 more distinctly from the Aurelise, Pelagioe, and Cyaneae, than the characters by 

 which they are distinguished from one another, and that the Charybdeae are again 

 very distinct from these two groups. Admitting further, what every naturalist at 

 aU familiar with the Acalephs will readily concede, that, whatever may be the 



