ATOLL A. 37 



sixteen canals branch, the branches of adjacent canals uniting in the mar- 

 ginal lappets. Thus there are, as Maas (: 03, p. 19) has shown for iV. picta, 

 two canals running into each marginal lappet. The radial septa extend 

 inward about as far as the ring furrow, where the canals become continuous, 

 to form the ring sinus. This arrangement of canals is in no way different 

 from the canal system of the Periphyllidae. Unfortunately both the distal 

 portion of the stomach and the gonads were destroyed in all three specimens. 

 The color of the entire gastro-vascular system of N. rubra is a deep amber 

 red. The jelly is pale yellowish. Vanhtiffen has reproduced ( : 02", taf. 1, 

 figs, i, 5) two excellent figures of this species from sketches made from the 

 fresh specimens. 



Atollidae. 



The only representatives of this family yet known belong to the genus 

 Atolla, Haeckel's genus Collaspis having been shown by Fewkes to be a 

 synonym. 



Atolla Haeckel, 1880. 

 sens. em. Fewkes, '86; Vanhoffen, : 02» ; Maas, '97, : 03. 



Coronata with a large and variable number of antimeres ; the tentacles 

 inserted much higher on the exumbrella than are the rhopalia. 



Our knowledge of this genus since its discovery by Haeckel ('80) has 

 been gained only step by step. And although, thanks to the studies 

 of Maas ('97, : 03, : 04") and Vanhoffen (: 02^*), the general anatomy and the 

 more important features in the histology of the genus have now been thor- 

 oughly worked out, the systematic relationships and specific characters of 

 its members are still by no means clear. The most important contribution 

 to this subject is that of Vanhoffen (: 02"), who was able to study a larger 

 series of fresh specimens from the collections of the " Valdivia " than any 

 other student has had access to. His conclusion, accepted in the main by 

 Maas (: 03, : 04'^), is that neither proportions of different parts, nor the num- 

 ber of antimeres is of any specific importance, but that the characters 

 which form the best bases for separating species are the presence or lack of 

 radial furrows on the central disc, and their number and form if present ; the 

 presence or lack of exumbral nettle warts ; and the size of the septal nodes. 

 Tiie presence or absence of radial furrows appears, not only from Vanhcjffen's 

 studies but those of Fewkes, ("89"), Maas, (: 04''), Mayer (: 06), and from the 

 present collection, to be an exceedingly stable character. It is true that 



