208 bulletin: museum of comparative zoology. 



the latter. But, as I have already pointed out (p. 205) the centripetal canals 

 in S. nauarchus are probably permanently blind, whereas in S. simulans they 

 come, through growth, to join the cruciform base of the manubrium. In S. 

 geometrica conditions in the adult, which alone is known, indicate that not 

 only do the older generations of centripetal canals join the base of the manubrium 

 but the youngest centripetals join the earlier formed canals, both radial and 

 centripetal, at varying heights. 



Tentacles. — In structure the tentacles resemble those of S. simulans ; their 

 better preservation allows confirmation of my previous description. They are 

 hollow, distensible to a length considerably greater than the bell height, and when 

 fully developed each bears at its tip a conspicuous nematocyst knob (Fig. 8). 

 The tentacles do not acquire this structure until fully grown. A similar terminal 

 knob was observed in S. simulans (Bigelow, loc. cit), p. 215), aud it is probable 

 from Maas's description that it occurs in S. geometrica. The basal swellings are 

 small (Fig. 3). In the appearance of the young tentacles in advance of the cor- 

 responding canals, S. nauarchus agrees with S. simulans. There are no ocelli, 

 nor have ocelli been observed in tins genus. 



The tentacles, as in both S. simulans and S. geometrica, appear to arise from the 

 exumbrella some little distance above the actual margin of the bell. This position, 

 however, is only secondary, aud is comparable to the exumbral origin of the 

 tentacles in the Olindiinae. The youngest tentacles stand free upon the margin 

 (Figs. 5-7). With growth, however, this primary position is concealed, for the 

 tentacles turn outward and upward, coming to lie in furrows of the exumbrella, 

 so that they apparently emerge from the surface of the bell some distance above 

 its margin. In S. nauarchus, at least, their bases never become entirely surrounded 

 by the gelatinous substance of the bell, as is the case in the Olindiinae, but the 

 exumbral furrows remain permanently open. 



Gonads. — The gonads in all the specimens are far advanced, large eggs being 

 visible in two individuals. In their main features they closely resemble those of the 

 two members of the genus previously known, being strictly interradial, entirely 

 discontinuous in the perradii, and consisting of double series of narrow and rather 

 regular transverse folds (Fig. 2). In addition to these transverse folds irregu- 

 lar projecting lobes are developed in three specimens (Fig. 1). Sections, how- 

 ever, show that such lobes are nothing more than regions of the sexual organ 

 which have made an irregular growth outward. The sexual organs are entirely 

 restricted to the walls of the manubrium ; they leave the labial region of the latter 

 bare. 



Color. — In life the gonads were deep brownish red, the terminal tentacular 

 knobs and basal bulbs pale yellowish. 



The evidence that S. nauarchus belongs to the intermediate fauna, and that it is 

 probably liberated from a deep-water hydroid, has already been given (p. 203). 



S. simulans was taken on the surface ; S. geometrica is known only from an in- 

 termediate haul. 



S. nauarchus is separated from S. geometrica by the fact that in the adult of the 



