HYDROIDS OF WOODS HOLE. 379 



cylindrical, gradually widening from base to margin, as shown in 

 Fig. 7, and are without appreciable constriction at base where 

 it articulates with the short, annulated pedicels, the annulations 

 occasionally extending some distance (rarely over entire body), 

 on the thecal walls, giving the impression of complete annulation 

 when viewed obliquely. The hydrothecae are very delicate, often 

 collapsing at the distal ends when being prepared for mounting. 

 There is a definite operculum, which often appears plaited, the 

 individual valves being more or less difficult to distinguish. I 

 have not determined their exact number with any degree of cer- 

 tainty. In many cases these valves exhibit the same aspect of 

 inversion as is the case with C. syringa, but I have not found 

 the presence of secondary rings or other marginal duplication as 

 in the latter species. Total length of pedicel and theca 0.2-0.3 

 mm. or an average of about 0.25 mm., by about 0.07 mm. in 

 diameter. 



Hydranth extremely small and delicate ; body elongate, cylin- 

 drical, with conical hypostome ; tentacles very delicate and 

 thread-like, usually ten in number, occasionally eight. 



Gonosome unknown. The examination of many colonies from 

 various localities failed to discover signs of gonangia. It may be 

 probable that like C. syringa this species has its breeding season 

 at some other time of year. 



Habitat. Found only associated with other hydroids, or 

 similar organisms, e. g., bryozoa, and hence is probably of com- 

 mensal habit. No evidence was found indicating parasitism. 



It is a pleasure to name the species, with his consent, in honor 

 of my friend and distinguished student of hydroids, Professor C. 

 C. Nutting. 



KERATOSUM COMPLEXUM, n. gen. and sp. (Figs. 8-10.) 

 On three successive summers there has been taken an organ- 

 ism at Crab-ledge which was variously assigned to the Porifera, 

 Bryozoa, and finally came to the writer. A glance at Fig. 8 

 will show how little there is from a superficial view to suggest 

 hydroidean affinities. Indeed it was only after sections had been 

 made, or maceration and dissection of the thing, that its true rela- 

 tions became evident. And it was only after considerable re- 



