ATOEELLA VANHOFFENI. 31 



the present species, however, it is set with numerous very prominent nettle 

 warts, the whole bell looking much like a small Pelagia (PI. 1, fig. 2; 

 PI. 11, figs. IS). These warts are not confined to the central disc, but 

 extend over the marginal region and lappets as well. They are merely 

 rounded eminences; it is not likely that their outline will prove of specific 

 importance. Structurally they consist of closely crowded ectoderm cells 

 among which lie nematocysts (PL 11, fig. 3 n.). 



The marginal lappets are oval, and very much longer than Maas repre- 

 sents them (: 03, taf. 3, fig. 16) ; but since he states that in the "Siboga" 

 specimen they were damaged, it is doubtful how closely the outlines in his 

 figure represent the natural condition. In the number of lappets, likewise, 

 the condition of his specimen was probably misleading, since he figures 

 twenty-four, two alternating with every tentacle and sense organ. Van- 

 hoffen, however, figures (: 02% taf. 3, fig. 11) the original specimen of the 

 genus with one lappet between each tentacle and sense organ, as is the case 

 in the present specimens, and this condition is, I believe, normal for the genus. 



The tentacles are about as long as the diameter of the bell. In A. subglobosa 

 Maas figures them as simply tapering ; in the present species, however, each 

 tentacle bears at its tip a knob-like swelling (PL 1, fig. 2). In longitudinal section 

 it is seen (PL 11, fig. 5) that this swelling involves both cell layers and that 

 the ectoderm contains many nematocysts. Similar, though less pronounced, 

 nematocyst swellings may also occur at other regions along the tentacles. 



The sense organs very closely resemble those of Atolla, in which genus 

 their structure has been so carefully worked out by Vanhoffen (: 02 :v ) that 

 repetition here is unnecessary. Their general form is shown in PL 11, 

 figs. 6, 7, and a somewhat diagrammatic longitudinal section in PL 11, fig. 8. 

 The octocyst and ventral bulbus, as well as the covering scale, are large and 

 prominent, but there are no ocelli, as already noted by Maas (: 03), who also 

 notes the resemblance to the rhopalia of Nausithoe. In finer structure 

 there is one important difference from the condition in Atolla. In the 

 latter, as figured by Vanhoffen (: 02", taf. 7, fig. 57) the exumbral surface of 

 the scale is covered with ordinary ectoderm, while in Atorella, in the same 

 region, the cells are so closely crowded as to form a well-defined thickening; 

 but whether this is sensory in function is doubtful. 



The stomach is shallow and flattened (PI. 12, fig. .',), the mouth parts short, 

 and the mouth opening with a slightly thickened lip. The four septal nodes 

 (PL 12, fig. J t ca) are narrow, the intervening ostia(os) correspondingly broad. 



