HYDKOMEDUSAE, SIPHONOPHORES, AND CTENOPHORES. 319 



The numbers of tentacles and of otocysts in four specimens of 

 different sizes are as follows : 



In the last two specimens a small portion of the margin was dam- 

 aged, so that at several tentacles the otocysts could not be determined. 



It is of interest that when paired otocysts are developed, they are 

 both distinguishable when the tentacle is very small. There is no 

 evidence that tentacles which have one otocyst during the greater 

 part of their history ever acquire a second one at a late stage. Single 

 otocysts are usually much larger than either of the components of 

 a pair. 



In the smallest specimen one of the quadrants is very narrow and 

 another disproportionately broad; the numbers of blind canals per 

 quadrant show a corresponding irregularity. Abnormalities are com- 

 mon in Olindias (Bigelow, 1909a). 



Subfamily Petasinae. 

 Genus NAUARCHUS Bigelow, 1912. 



Petasidae with six radial canals, but without centripetal canals; 

 manubrium short and flat, without distinct gastral portion; mouth 

 surrounded by a simple circular lip; gonads leaflike; tentacles of 

 one kind only, corresponding to the primary tentacles of Olindias, 

 their basal ends lying in furrows of the gelatinous substance so that 

 they appear to emerge from the exumbrella ; with terminal nemato- 

 cyst swelling; otocysts are free clubs. At first sight the shallow 

 manubrium with its simple, circular lip (pi. 43, fig. 1), suggests an 

 Halicreid, the presence of six radial canals, 1 and the flat oval leaflike 

 gonads, a geryonid, such as Geryonia. But the absence of any trace 

 of peduncle separates Nauarchus from the latter, the structure of oto- 

 cysts from the former, its sense organs with spherical capsule and 

 inclosed sensory stalk, being entirely different from the large sense 

 clubs with series of columnar entoderm cells which characterize all 

 known Halicreids. And in the structure of the tentacles there is an 

 equally important difference, for in all Halicreids in which these 

 organs have been described they consist of soft proximal and stiff, 

 spinelike distal portions (1909a), besides arising free from the mar- 



1 One of the specimens is abnormal, there being only four canals at the margin of the 

 stomach. One of these, however, soon divides into three, though only two of the latter 

 reach the circular canal. 



