38 IDYIA CYATIilNA. 



I have observed ; but as the tubes of the other genera are so soon 

 hidden by the rows of locomotive flappers, it becomes more difficult to 

 follow this separation than in Idyia, where the ambulacra retain always 

 a great size, and develop faster than the ro\^'s of flappers which cover 

 them. The longitudinal ambulacra mcrease rapidly in length, pushing 

 their way through the gelatinous mass (Fig. 56, c) till they reach the 

 level of the mouth (Fig. 57) ; they then bend inwards (Fig. 58) till 

 they meet the lateral chymiferous tube. The lateral ambulacra go 

 through the same process (Figs. 58, 59) ; and thus we have formed, by 



the junction of the ambulacra 



Fig. 61. Fig. 62. • i i i 



With the lateral chymiferous 

 tubes, a circular tube round the 

 mouth. (Fig. 60.) The distinc- 

 tion between the longitudinal 

 and lateral ambulacra is always 

 maintained by the length of the 

 rows of locomotive flappers which 

 cover the ambulacral tubes. The 

 frmged abactinal apparatus is in 

 the young a circidar ring ; afterwards it has four folds developed at 

 the extremity nearest the sensitive bidb (Figs. 59, 61), which soon 

 become fringes similar to those of the adult. Shortly before the circuit 

 is thus completed (Figs. 58, 59), the ambulacra of the young Idyia give 

 out a few lateral processes, the first traces of the ramifications of the 

 ambulacra of the adult (Fig. 62), which become more and more numer- 

 ous until the processes branch as in Fig. 60. 



The short chymiferous tubes are, as in Pleurobrachia, on each side of 

 the lateral tubes, while in Bolina this is not the case, the long tubes 

 being near the short transverse axis. 



Coast of New England, and northward to Bay of Fundy (Agassiz). 

 Catalogue No. 368, Nova Scotia, Anticosti Expedition, 1861. 

 Museum diagrams Nos. 6, 7, after Alex. Agassiz and L. Agassiz. 



Idyla cyathina A. Agass. 



Idyia cyathina A. Agass. ; in Agassiz's Contrib. Nat. Hist. U. S., Vol. III. p. 296. 1860. 



This species differs from the Idyla roseola Agass. of the coast of New 

 England, by the sudden widening of the spherosome from the abactinal 

 pole. It is widest at two thirds the distance from the mouth ; it then 

 tapers as suddenly for another third of the distance to the mouth, and 



Fig. 61. Fig. 57, seen from the abactinal pole. 



Fig. 62. Adult Idj-ia, reduced in size one half. «, anal opening; b, lateral radiating tube ; 

 c, circular tube ; d, e, f, g, h, vertical rows of flappers. Seen from the broad side. 



