138 repokt— 1884. 



Genus Idmonea, Lamouroux. 



I<hnonea, Lamx., Blainville, Milne-Ed., Jolinston, Reuss, D'Orbigny 

 (part), Busk. ; Iietepora, (pt.) Goldfnss, Lamk. ;Diastopora, (pt.) Michelin, 

 Tabulipora, (pt.) Lamk. ; Crisina, (pt.) D'Orb., Smitt ; Tubulipora, sub- 

 genus Idmonea, Smitt. 



' Zoarium ei*ect and ramose, or (rarely) adnate ; branches usually 

 triangular. Zocecia tubular, disposed on the front of the branches, 

 ranging in parallel transverse or oblique rows on each side of a mesial 

 line.' — See Hincks, p. 450 ; Busk, ' Crag Polyzoa,' p. 104. 



This peculiar genus seems to have originated in early Mcsozoic times, 

 but the species described by Lamouroux as I. triquetra, as occurring in 

 the Jurassic rocks, especially in this country, is far less specialised than 

 those forms found in the Cretaceous rocks of Maestricht, and in the 

 Faxoe Limestone of Denmark. The unusual character of some of the 

 species described by Goldfuss as Retcpora clathrata and B. disticha, 

 induced Hagenovv to break up the forms grouped together by Goldfuss, 

 out of which several new species were founded, described and figured. I 

 do not say, after having studied the Faxoe material, that Hagenow was 

 wrong in his redistribution, but I think that even he has given us more 

 species than were needed or that the doubtful character of some of 

 the forms warranted, but his beautiful figures have materially assisted 

 the student in mastering the details of the group. Yet it seems 

 to me a rather invidious practice, in the present state of our 

 knowledge, to criticise unfairly the labours of other authors on this 

 peculiar group of fossil forms. It is not a mere matter of opinion as to 

 whether this and that form are identical, because unless there is a 

 sufficiency of material to connect by intermediate links form and form, 

 mere opinion in this direction is useless. I have hundreds of specimens of 

 Beuss's Idmonea cjracUlima from the Montecchio Maggiore beds, and it is 

 quite possible to erect two or more species out of the various specimens 

 accordingly as we accept the young or the matured stages as types. As 

 I have been able to trace this form from a single elongated cell on each 

 side of the mesial line up to four and five cells on each side of the mesial 

 line, I can on!}' say that mere growth is a fallacious factor in the deter- 

 mination of a species. In the enumeration of the following I shall take 

 into consideration other special features, leaving the number of cells in 

 the branch for woi'kers to deal with separately, if they so desire. I shall 

 take the species as I find them in the works of authors accessible to me. 

 As my friend Mr. A. W. "Waters has gone over the Tertiary species for 

 his work on the Bryczoa of the Bay of Naples, I shall take his references 

 to fossil species as work accomplished, because he has had a fuller access 

 to foreign works than I could possibly obtain. 



Before passing on to the numerous fossil forms described by authors 

 it may be well to dispose of the two recent species which are now pretty 

 well known to zoologists. 



23. Idmonea atlantica, Forbes, MS. See Busk, ' Cyclostomata ; ' 

 Waters, ' Bay of Naples Bryozoa ;' Hincks, ' Brit. Mar. Polyzoa.' 



' Zoarium. irregularly branched, branches triangular, cells oiie, four, 

 five in each series, the, innermost the longest, dorsal surface of branch 

 not perforate ' (Busk) ; ' dorsal surface, lineated and minutely punctate ' 

 (Hincks) ; peristome entire .... The large tubular cells, mode of 



