14 THE HYDROIDS. 



Thuiaria tubuliformis Marktanner-Tumeretseher. 

 Plate 9. 

 There are about 20 colonies attached to pieces of a bivalve shell from 

 Perico Island. The specimens are from 25 to 40 mm. in height, and several 

 have gonangia. The internodes are described as " bearing a branch and two 

 hydrothecae on one side and a single hydrotheca on the other." Some of the 

 internodes in these specimens bear a branch and three hydrothecae on one 

 side and two on the other. The tendency of the hydrothecae to arrange 

 themselves in groups, mentioned by Nutting, 1 and especially so toward the 

 distal ends of the branches, is quite pronounced. The localities for this 

 species hitherto reported are all from the Atlantic side of the continent, 

 — Brazil, Florida, and the Bahama Banks. This is yet another instance 

 of the same marine invertebrate occurring on both sides of the Isthmus of 

 Panama. 



Sertularella tropica Hartlaub. 



Plate 10, Figs. 1-3, 3 b. 



A few small, fragmentary specimens attached to a chitinous worm tube 

 came from Station 4047, Latitude, South; 4° 33', Longitude, West, 87° 42.5'. 



Depth, 2005 fins. Trawl, open net tow to surface from 800 fms. 



In Nutting's table of the bathymetrical distribution of the Sertularidae, 

 the greatest depth recorded is 1168 fms., and it is interesting to note that it 

 is a record of this species, and in the Eastern Pacific not far from the Equa- 

 tor. As the worm tube to which this specimen is attached is uninhabited, it 

 may have been floating and have been picked up by the tow net on its way 

 up from the 800 fm. line. 



This species was first named Sertularia variabilis by myself in 1894, an 

 unfortunate christening, as that specific name was preoccupied. Hartlaub 

 renamed it tropica in 1900, and changed it into the genus Sertularella. These 

 two genera are not distinct enough to warrant a further complication of the 

 synonymy by calling this again Sertularia. The determination of genera in 

 the Hydroida is perhaps peculiarly unsatisfactory, inasmuch as there is often- 

 times only the perisarc from which the description is written, and in some 

 cases only that of the trophosome. The recognition of genera being largely 

 a matter of convenience, and as the fuller knowledge shows us ever more 



1 Special Bulletin, Smithsonian Institution, 1904, Part 2, p. 70. 



