NO. 3 fraser: hydroids 137 



Description of one new genus, tivelve new species, and the gonosome of 



two other species. 



PPerigonimus gracilis, new species 

 Plate 19, Fig. 1 



Trophosome. — Colon}^ slender, sparsely branched, the branches com- 

 monly coming off at an acute angle with the stem and the pedicels simi- 

 larly from the stem or branches; the largest colony observed was 5.5 

 mm. high. Perisarc never very thick, thins out to end almost impercep- 

 tibly below the base of the hydranth, the surface smooth or slightly 

 wrinkled. Hydranth long and slender but considerably greater in di- 

 ameter than the pedicel. Tentacles 10-12. 



Gonosome. — Not observed. 



Note. — It is quite possible that this is the species of Perigonimus 

 that Hartlaub described and figured, as Perigonimus sp. in Die Hy- 

 droiden der Magalhaensischen Region und Chilenischen Kiiste, 1905, 

 p. 532, as it bears some resemblance to his figure "0," but it also bears 

 a resemblance to his figure "Ka," which, for some reason difficult to 

 understand, he labels "(?) Perigonimus repens Wright." 



Perigonimus robustus Fraser 

 Plate 19, Fig. 2 



Perigonimus robustus Fraser. Hyd. of the 1934 Hancock Exp. 1938, 



p. 17. 



Trophosome. — For description see original reference. 



Gonosofne. — Medusa-buds grow singly from the hydranth pedicels, a 

 short distance below the hydranths themselves, with short, annulated 

 pedicels. The medusa-bud reaches to, or a little above, the margin of 

 the hydranth tube and is of much the same diameter as this margin. 



Hydractinia rugosa, new species 

 Plate 19, Fig. 3 



Trophosome. — Nutritive zooids, not closely placed, arise from an 

 encrusting coenosarc that does not show any network at the surface; 

 those most fully extended reach a height of nearly 2 mm. There are 

 commonly eight tentacles ; either four of these are much longer than 

 the other four, or they are extended while the others are contracted, as, 

 in the preserved material, this difference in size is definitely indicated. 



