CHATTER FOURTH. 



THE GENUS PELAGIA AND ALLIED GENERA. 



SECTION 1 



THE FAMILY OF PELAGID^. 



The genus Pelagia, as defined by Peron and LeSueur, embraces species which, 

 in my estimation, belong, unquestionably, to different genera, if the differences noticed 

 between the other genera allied to Pelagia, thus far admitted by naturalists, afford 

 any standard of appreciation of generic differences. Be this, however, as it may, 

 Pelagia and Chrysaora constitute a natural family, first recognized by Gegenbaur, 

 and characterized by him, in the "Zeitschrift fiir wissenschaftliche Zoologie," Vol. 8, 

 p. 210, as distinguished from the other families of Acraspeda, by the pouch-like 

 appendages of the stomach or main cavity, to which he adds the more or less 

 bulging form of the disk and the oral appendages, varying from the simplest form 

 to that of four-lobed arms. Correctly as the family is circumscribed here, the 

 characters assigned to it are insufficient to distinguish it from the Cyaneidae, in 

 which there are also radiating pouches, and in which the other structural characters 

 vary in the manner ascribed by Gegenbaur to Pelagidte. It is my opinion that the 

 essential structural characteristics of the Pelagidce, in their adult condition, consist in 

 a combination of spheromeres peculiar to them, there being four ambulacra! pouches 

 in the prolongation of the four corners of the mouth, between the marginal inden- 

 tations of which there is an eye, and four interambulacra, each one of which consists 

 of three pouches, similar in dimensions to those of the ambulacra ; the central one 

 of these pouches has an eye, in the indentation between its lobes, while the other 

 two have single tentacles, or sets of tentacles, variously combined. The genital 

 organs consist each of three lobes, the middle of which (PI. XII. Fig. 2, b h) is in 

 the radial prolongation of the middle interambulacral pouch, while the two others 



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