CHARACTERISTIC DEEP-SEA TYPES. ACALEPHS. 



133 



not more than five genera were known from the Western At- 

 lantic, while at the present time that number is more than 

 doubled. 



Of the aberrant group of Rhizophysidse no less than three 

 species are now known from the Gulf Stream. One of the most 



Fig. 427. Atolla Bairdii. f. (Fewkes.) 



characteristic species of the group, Pterophysa, has been men- 

 tioned in the chapter on the Pelagic Fauna. 



Agalma Okenii (Fig. 428) is common in the Gulf Stream ; 

 it is easily recognized by the rigid nature of the colony, and 

 by this can at once be distinguished from the Agalma found 

 at Newport. The end of the axis opposite the float bears thick 

 covering scales, while in the Newport Agalma the scale is leaf- 

 like, and not cubical or polygonal. 



One of the least known genera of Physophorse is the genus 

 Athorybia. It is remarkable in many ways, and differs from all 

 known physophores in the character of its covering scales and 



