T 



138 



REPOKT — 1884. 



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i<i| 





Genus Idmonka, Lamourous. 



Iilninnea, Lamx., Blainvillc, I'llilno-Kd., .lolinstoii, Reus.s, D'Orhii^'iiy 

 ('l).u'fc),l{iisk. ; Jicfi'pora, (pt.) Goldfnss, Liiiiik. •,J)insfop(>ra, (pt.) .Micliflin, 

 'riiJjidijjdrd, ([)t.) Liuiik. ; Cfitfii/d, ('))('.) D'Orb., Siuitt ; Tnhitl'qiora, sub- 

 genus Idvioii'Jii, Smitt. 



'■ Zoariiua erect and ramose, or (rarely) aduale; brandies usually 

 trianrjular, Znntrla tubular, disposed on the front of the branches, 

 rauyinrr in parallel transverse or ()i)liq>ie rows on each side t)f a mesial 

 line.'— Sec Hincks, p. 450 ; Busk, ' Cra^- Polyzaa,' p. 1(»1-. 



This peculiar i^-euus seems to have originated in early Mcso'/dic times, 

 but the speci !S described by Ijamouroux as J. 'n'qiwtni, jis occurring in 

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

 those forms found in the Cretaceous rocks of ^Alaestricht, and in the 

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

 species descri'jed by Goldfuss as .Uclepora dnHirata and A*, distichn, 

 induced Hagenow to break u[) the foi.us grouped togetiier by Goldfuss, 

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

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

 wronsr in his redistribution, but I think that even he has tiiven us more 

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

 the forms wari'anted, but his beautiful figures have niatei'ially assisted 

 the student in raastei'ing the details of the group. Yet it seems 

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

 knowledpfc, to criticise unfairly the labou'-s of other authors on this 

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

 whether this aiul (hat form arc identical, because unless there is a 

 sufficiency of material to connect by intermediates links foi-m and form, 

 mere opinion in this dii'cction is useless. 1 have hundreds of specimens of 

 Reuss's Idiiiiiiii'it (/i-aci!/iiii(iivoni the Montecchio Maggioro beds, and it is 

 quite possible to ei-ect two or more species out df 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 sino-le clomjated cell on each 

 side of the mesial line up to four and live cells on ea(di side of the mesial 

 line, I can only say that mere growth is a fallaeiuns factor in the deter- 

 mination of a species. In the enumci'ation of the following I shall take 

 into consideration other s])ocial features, leaving the inimber of cells in 

 the branch for workers to deal witli separately, if they so desire. I shall 

 take the species as 1 liml them in the works of authoi's accessible to me. 

 As my friend jMr. A. V^. AVaters has gone over the Tertiary species for 

 his work on the J>ryo;,oa of the Bay of Naples, I shall take his references 

 to fossil species as woik accomplished, because ho has had a fuller access 

 to foreign works than I cuuld ]iossibly obiain. 



Before passing on to tlu! numerous fossil form:, described by authors 

 it ma}' be well to dispose of the two recent species which are now pretty 

 well known to zoologists. 



2;j. In:\ioNK.v atlantica, Forbes, j\lS. See Busk, ' Cyclostomata ; ' 

 Waters, 'l:?ay of Naples Bryozoa;' Hincks, 'Brit. Mav. Polyzoa.' 



' Zd/iriniu. irregularly branched, branches triangular, cells one, four, 

 five in each series, the, innernujst the longest, dor.sal surface of branch 

 not perforato' (Busk) ; 'dorsal surface, lineatedand minutely punctate' 

 (Hincks) ; peristome entire , . . . 'I'ho largo tubular cells, mode of 



