Chas. W. Hargitt 



characters found in a Hydroid taken by bim in August of that year 

 at Manger, Norway, at a deptb of from 20 — 30 fatboms. The name 

 was based upon tbe oceurrence of the gouads surrounding tbe hydro- 

 caulis, a cbaracter now well kuown to bave no geueric value wbat- 

 soever, as it is sbared by many otber genera. 



I cannot ascertain wbetber tbe species described by Sars has ever 

 been noted by subsequent students of the Hydroidea. Allman^ ex- 

 pressly states that bis description of it is based upon characters 

 published by Sars. Weismann 2 also refers to this species with a 

 degree of conservatism which might clearly indicate a doubt as to 

 Sars' species. ludeed neitber from bis descriptions nor bis figures would 

 one recognize typical members of tbe genus as at present known. 

 However, Allman cousiders tbe Hydroid as entitled to generic rank, 

 and whatever niay be the doubts as to its affording a typical repre- 

 sentation of the genus, the genus itself is one of the best defined of 

 the entire family of which it forms a member. 



The generic characters given by Hincks^ seem to me to be, 

 upon the whole, the most distinctive, and I reproduce them bere, add- 

 ing what seems necessary to adapt them to our present knowledge 

 of the genus: 



Coenosarc sheathed in a chitinous, sub-chitinous, or gelatinous 

 perisarc; hydrocaulis branching or simple, from a filiform hydro- 

 rhiza; hydranths fusiform, with a single verticil of filiform tentacles 

 surrounding the base of a conical hypostome; gonophores developed 

 from the coenosarc. Gouozooids free and medusiform. Umbrella 

 deep bell-shaped; manubrium short; radiating canals four; marginal 

 tentacles two or four, often iucreasing with age, springing from non- 

 ocellated bases. 



The modifications included in the characters are made necessary 

 by reason of structures peculiar to at least two of the more recently 

 described species, namely, P. cidaritis^ Weismann *, and P. Jonesii^ 

 Hargitt & Osborn ^ In both these species the perisarc is in what 

 may be regarded as a primitive, non-differentiated, gelatinous con- 

 dition; a sort of slimy ectoderma! secretion, not yet solidified, but 



1 Gymnoblastic Hydroids 1871 pag. 323. 



2 Die Entstehung der Sexualzellen bei Hydromedusen 1883 pag. 115. 



3 British Hydroid Zoophytes Vol. 1 1868 pag. 89. 

 * Op. cit. 



•'' American Naturalist Vol. 28 1894 pag. 27. 



