310 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



dana) by very small stomach. The Aequoreas in the present collec- 

 tion all have smooth subumbrella, a broad stomach, and many more 

 canals than tentacles ; but they are separable into two groups by the 

 following structural characteristics: 



a. Specimens with triangular basal bulbs, which do not clasp the 

 exumbrella ; without excretory papillae, with about 11 or 12 times as 

 many canals as tentacles; with a good deal of anastomosis of the 

 canals near their tips. 



b. Specimens with basal bulbs clasping the exumbrella more or 

 less ; with excretory papillae, with from 4 to 6 times as many canals 

 as tentacles, with little if any anastomosis of canals. 



I have already attempted a temporary revision of the Indo-Pacific 

 Aequoreas (1909&, 1913), and these two forms agree very well with 

 two species there recognized, namely, pensile and macrodactylum. 

 Both of these have likewise been studied by Maas (1905), while 

 Browne (1904), writing almost simultaneously, recognizes both, 

 though he used a new name, maldivensis, instead of macrodactylum. 

 They are united by Vanhoffen (1911) as pensile. But the presence 

 or absence of excretory papillae is significant. These have never been 

 recorded for pensile, though Browne (1905) made a special search 

 for them, and of course I have looked for them carefully in the pres- 

 ent series. A. pensile is further distinguished by the extraordinarily 

 thick biconvex disk, an excellent " field mark." On the other hand, 

 the wing-like lateral extensions of its tentacular bulbs prove to be 

 less constant than earlier studies suggested. The characters of a 

 series of each are given below (pp. 312, 314). 



Macrodactylum is very closely allied to the widely distributed 

 Aequorea aequorea. As a rule, the numbers of tentacles and canals 

 are more nearly equal in aequorea than in macrodactylum, as I have 

 pointed out (1913, p. 37) ; but there is no discontinuity between the 

 two in this respect, nor is there anything in the structure of stomach 

 and mouth, of gonads nor in general foim to separate them. 



The shape of the tentacular bases, clasping the exumbrella, is the 

 most distinctive feature of macrodactylum. But it is not possible to 

 draw a sharp line between it and aequorea in this respect, for, as I 

 have already pointed out (1913, p. 37), the specimens show all stages 

 from clasps "as pronounced as figured by Maas (1905) for macro- 

 dactylum, to a condition where it is doubtful if they are present or 

 not." Conversely, some of the tentacle bases in a specimen of 

 aequorea from Naples have distinct clasps. And in an excellent speci- 

 men from Puget Sound, 40 mm. in diameter, with 77 canals and about 

 66 tentacles (a few are lost), some of the tentacular bases are of the 

 " aequorea," others of the " macrodactylum " type. Thus there is no 

 discontinuity in this respect, any more than in the number of ten- 



