THE SERTULARIDJ5. 61 



I have not seen this species and quote the original description entire. It i.- quite possible that 

 the species is identical with X rtuLaria /'/< //<//<////;/*, which was collected by Yersluys at the same 

 place, l)iit tliis point cannot lie determined except by a comparison of the two types. 



Tij[><:. In the Museum of Comparative Zoology, Cambridge. Massachusetts. 



SERTULARIA EXIGUA Allman. 



( 1'liite VI, litr. I!, i 

 Hi'i-lii/iii-iii . ill/mi AI.I.MAS, MI-MI. MM.-. CoMip. X.ool., V, No. -, 1ST", ]i. L'l. 



" 7'fii/t/iiixotii, . - Hydrocaiilus minute, simple. attaining a height of about one-fourth of an 

 inch; internodes very short, not prolonged bv an attenuated continuation below the pairs of 

 hydrothecic. Ilydrotheca- opposite, not tumid below: free and divergent on their distal half, 

 aud with the opposed sides of each pair parallel to one- another." 



Gonosome. Not known. 



Dixtrlliutinn. - Off Cape Fear, !i fathoms (Allman). 



I have not seen this species and have copied the original description entire. 



Ti/j>f. In the Museum of Comparative Zoology, Cambridge, Mas.-achiisetts. 



THUIARIA Fleming (modified). 



Ti'iifiliiiNintii . II vdrotheca- normallv subopposite to alternate, and more than two to each 

 internode. Intel-nodes vary greatly in length. Ilydrotheca' with smooth margin, or with one 

 or two teeth, usually more or less immersed in the hydrocaulus. Operculum of one ahcaulinc 

 dap. or of two flaps. 



(iiHioxiHH,; (ionangia oval, with large terminal aperture, imoriiaiuented or with one or two 

 spines on the shoulders. 



As before intimated, this genus as established by Fleming (I*-*) was very much restricted, 

 containing but two species, and based solely on the immersed condition of the hydrothec;v. There 

 was no change made by either Johnston (1S4S) or Hincks (iSliS). 



In his diagnoses of new genera and species of hydroids Allman 1 adopted a new 

 criterion for the genus, holding that the best character was based on the division of the 

 hydrocaulus into internodes, there being an internode to each pair of Ilydrotheca? in .V /'///A//'/*/. 

 Sertnl/ri'i'Iln and Ilijilmxiii. "while in T/minrin the joints occur at distant and, for the most part, 

 irregular intervals, thus leaving numerous hydrotheca' to be carried on each internode." He was 

 thus led to admit, such species as S,-rtnl<iri<t <tr<i< nt< : <i and X. cupressina into the genus, as is done 

 in the present work. In his report on the hydroida of the Challenger Kxpedition (Iss.s) Allman 

 maintains this same position. 



In his Catalogue of Australian Hydroid Zoophytes (1884) Hale givesa further criterion. His 

 definition of Tlminrin is "Zoophyte plant-like -Hydrothecse biserial. not in pairs, usually more 

 or less immersed." He points out the distinction between the hydrothecse being in two series 

 and being in pairs. This, however, often seems to depend on the thickness of the hvdrocaulus. 

 If it is very thick there are two series, while it often happens that on the more .-lender distal 

 branches the hydrotheca' are regularly subopposite or alternate, or in pairs, as Hale n-e- the term. 



Levinsen in his Meduser, Ctenophorer Og Hydroider fra (ironlands Yestkyst. p. 1!':-!. defines 

 the genus as follows: "Apertura hydrotheca- rotundata (ovalis yel semicircularis). 'Collare' et 

 'dentibus' nullis instructa. In margine exteriore (abcaulim) valvula opercularis allixa est." Like 

 the other genera founded on the character- of th<' margin and operculum. this one includes forms 

 that the present writer and others regard as generically distinct, a- -V, /,/,//'//,<//* <i/>, rait />,<</ 

 Levinsen, and excludes others that are very close! \ related, as 77/ ///,///,/ <l<ilH or T. rlixl,i 

 Clark or T. tliui<tri<>i<l, * ('lark, the latter being a typical tlmiarian. but with an adcaulinc 

 operculum. Moreover in some cases certain part-, of a colony would belong to 77/ ///////,/. and 

 others not. were the definition of Levinsen adhered to. as /'. rulmxlii. in which part of the 



'Journal of tho l.inn.-i-ui Society, /.ooloi;\ . XII. 1S74, |-. L'tST. 



