358 DONNELL BROOKS YOUNG 



evenly rounded, the lateral margins symmetrical; the surface 

 of the dorsal region sometimes smooth, sometimes longitudinally 

 ribbed; anal uncini and styles variable in character and number, 

 usually from three to seven or eight recurved and occasionally 

 fimbriated uncini inserted in the right posterior cleft but not 

 more than two or three in the opposite one ; each of the fascicles 

 occasionally supplemented by one or two fine simple setae." 



This description is a very inclusive one, and it seems probable 

 that some of the variations mentioned are in reality separate 

 species. Sufficient data are not given, however, to be sure of 

 this. Unfortunately, no mention is made of the nuclear com- 

 plex or of the exact arrangement of the cirri. 



An examination of the drawings which Wallengren ('02) 

 (fig. 8) made in his studies of the regeneration of the cirri during 

 division shows an animal which differs in shape and number and 

 arrangement of cirri from that which Calkins used for his work 

 at Roscoff (fi-g. 12). A detailed study of living material would 

 probably show them to be different species. 



Three forms of Uronychia are to be recognized at Woods Hole. 

 These differ in size, nuclear complex, and arrangement of cirri. 

 The largest of the three corresponds most closely to Stein's de- 

 scription of U. transfuga, and is probably the same one which 

 Calkins used at Roscoff. This species was seen only once during 

 1919, but was found in abundance in 1920. It appeared too 

 late, however, for experimental use. It may be described as 

 follows (fig. 7) : 



Description of Uronychia transfuga 



Carapace 130 to 170 m long by 100 to 120m wide and 25 to 

 40 M thick. Anterior and posterior ends rounded. Carapace 

 arched and smooth. On the posterior ventral border is a cavity 

 in which are inserted two heavy curved cirri and a cluster of from 

 five to seven small straight ones. From the right ventral pos- 

 terior cavity originate four or five straight cirri. From the right 

 dorsal posterior cavity project three heavy curved cirri. The 

 anterior cirrus-hke membranelles, seven to nine in number, are 

 set in slight depressions on the anterior edge of the carapace. 



