258 PROCEEDINGS OF THE yATIOXAL MUSEUM. tol. 43. 



NAUARCHUS, new genus. 



The three specimens on which this new genus is based are extremely 

 interesting, for while their relationship to the Olindiinaeis patent, the 

 gonads are of the Geryonid type, and the manubrium is suggestive 

 of that organ among Halicreasidse, a conformation without parallel 

 among Petasidae. 



The genus may be defined as Petasidae with 6 radial canals, but 

 \v-ithout centripetal canals; manubrium short and flat, "s\"ithout dis- 

 tinct gastral portion; mouth surrounded by a simple circular lip; 

 gonads leaflike; tentacles of one kind only, corresponding to the 

 primary tentacles of OUndias, their basal ends lying in furrows of the 

 gelatinous substance so that they appear to emerge from the exum- 

 brella; with terminal nematocyst swellings; otocysts free clubs, be- 

 tween the bases of the tentacles and the exumbrella. 



Type of the genus. — Nauarchus Tialius, new species. 



NAUARCHUS HALTOS, new species. 



Station 5456, 120-0 fathoms, 3 specimens, the largest 12 mm. in 

 diameter, the other two smaller, but too contracted for measurement. 

 All three are so badly crumpled that it is impossible to make a photo- 

 graph of the general habitus. But all were well preserved anatomi- 

 cally. The largest specimen may be taken as the type. 



The gelatinous substance is thick centrally, thimier near the 

 margin, the bell ca^dty shallow (at least after preservation). The 

 velum is unusually broad; its circular muscles well developed. In 

 general appearance the specimen strongly suggests a Halicreid, as, 

 for instance, EomcBonema alha. And the likeness is heightened by 

 the gastric system. 



The manubrium is small, 3 mm. in diameter; hexagonal in out- 

 line, its lower wall hardly at all pendent ; the mouth surrounded by 

 a simple thickened circular lip. 



There are six broad radial canals, subtending equal arcs of the bell 

 margin. The six gonads occupy the greater length of the radial canals, 

 though leaving their extremities, distal and proximal, free. They are 

 flat and leaflike, exactly like the corresponding organs in Liriope, 

 and oval in outline. The specimen is apparent!}' a male. 



Marginal organs. — There are 12 solid tentacles, 6 radial and 6 inter- 

 radial. The radials are larger, and one of the interradials is so small, 

 that it was ob^'iously formed very recently. Only two large tentacles 

 are intact throughout their length, and both of these are interradials. 

 For over four-fifths of their length they are smooth-walled, but near 

 their ends they bear a series of about 20 prominent annulations, 

 composed of nematocysts, and at the tip there is a prominent sub- 

 spherical knob of closely crowded ectodermic cells radially arranged. 

 But this is not flattened to form a ''sucker," as in Gonionemus. The 



