Chap. II. CTENOPHORiE SACCATE. 193 



concentric systems of motoiy cells in all the eight spheromeres. It is impossi- 

 )>le to read the true family characters of the Eangiidoe and Neisida; in Lesson's 

 indifferent descriptions, and but for the ftxmiliarity I have acquired with the different 

 types of Acalephs, I shoidd not have ventured to point them out at all ; but I 

 hope, in this way, to call the attention of naturalists more directly to these curious 

 species. However, while I indulge in this joiece of presumption, I feel compelled 

 to repeat a remark already made elsewhere, that the difference between character- 

 izing a tlimily by its peculiar structural form and simply pointing out its existence 

 and probable differences should never be lost sight of When considering the North 

 American species of this type, we shall also examine how far Gegenbaur is correct 

 in referring all the true Beroidoj to a single genus, Beroe Brown. Meanwhile, I 

 would only call attention to the foct, that Lesson has referred to this genus many 

 species which belong to the family of Cydippida?, and were mistaken by him for 

 genuine Beroidte, because the specimens he noticed had lost their tentacles : such 

 are most, if not all, his Beroes Melonides. 



We liave thus three families of Ctenophorce Eurystoma3 : the Beroid.e proper, 

 the Neisid^, and the Rangiid.e, one of which only — the Beroida^ — is satisfactorily 

 known. 



SECTION III. 



THE NATURAL FAMILIES OF THE CTENOPHORCE SACCAT^E. 



As was shown in a preceding section, the Ctenophoras Saccatas constitute a 

 natural sub-order, corresponding to the genera CaUianira and Cydippe of Peron and 

 Eschscholtz, to the families Callianiridaj and Cydippida3 of Gegenbaur, and to the 

 tribe CydippEe, and part of the trilje CaUianira;, of Lesson. We have now to 

 consider the natural limits of the families of this group. 



The genus CaUianira of Peron, from which Eschscholtz derived the name of his 

 family Callianirida^, — in which, besides CaUianira, he includes Cydippe and Cestum, 

 — has not been observed for more than half a centurj^ Our knowledge of these 

 Acalephs is therefore limited to the few and rather indifferent statements included 

 in the characteristics of the genus as described by Peron, and some other remarks, 



uniformly arched, an unquestionable diffei-ence be- difference in the curve of corresponding rows of the 



tvveen the anterior and the posterior rows on one same pair among the anterior and posterior ones, 



side and the lateral rows on the other side; and as well as among the proximate lateral rows of 



a practised eye cannot fail to perceive a marked the same side. 

 vol.. III. 2o 



