low ol' |)l;ili*s on cmcIi side of llic middle one liiis one half williin llie same zoo'cium, 

 and llie olher hall' witiiin llie adjoiniiifi; zocx'cium. These apparently liall" parts do 

 not ix'loMf^ lo each other however, as each of them j)asscs over into and joins at 

 a rif^hl angle lo one of the small plates of which each lateral wall consists. That 

 two adjoining rows of half plates seen from the surface of the colony can look 

 like a row of whole plates, is due |)arlly lo the fact that they lit exactly btleach 

 other, partly that from the surface we cannot see the halves adjoining one another 

 in the vertical walls. Further, as the zod'cia in one layer of the colony alternate 

 willi those in the second layer, a median row of ])lates in one layei- will corre- 

 spond lo a donlile I'ow of adjoining half plates in the olher, and Ihe two ad- 

 joining half plates are in size almost exactly like Ihe opposite plate. The ter- 

 minal wall is divided into two lateral halves hy a suture, running medially through 

 Ihe single rosetle-])lale. At the borders helween Ihe single longitiulinal rows we 

 also lind small iincalcilied inlerspaces, while the plales in Ihe single rows are 

 separated by narrow sutures. 1 have in Iwo previous |)apcrs ' designated this 

 manner of calcilicalion as circular, because the calk pai'licles in Ihe individual 

 small plales are circularly arranged round a small condensed shining spot, which 

 we might call Ihe 'Centre of calcilication«, and which in Ihe angularly bent plates 

 is placed in Ihe angle helween Ihe Iwo pieces of each plale. 'l"he circular arrange- 

 menl is most distinct close to Ihe centre and vanishes gradually furlher out. 

 Still, more or fewer zoa-cia show a less regular arrangemenl of the small plales 

 in the marginal pari of the colony, and Ihe same can be seen in scattered zoo'cia 

 in olher parts of Ihe colony. The basal suil'ace may Ihen either be broken up 

 into an irregular mosaic of larger or smaller jjlates of dilTerenl sha|)e, or llie 

 median row of plales may be missing or represented only by very few ])lates. 

 We can even here and there lind a cell-mosaic. I have found a plate-mosaic 

 like Ibis on Ihe lateral walls in I'liislra foliiiceii (I'l. .\l.\, lig. U b), on Ihe basal 

 wall in I'orclld sdccdhi, I'or. roiiiiircssd, Smilliiid tiisiiiiKisa. Sni. pdUiuild (I'l. .\IX, 

 lig. 5 b), .S';)(. liiiedris, Discopord pin'oiiclla, l-liislra sririilald, Fl. piscifoniiis as well as 

 on Ihe front wall of liii>cisiiild iiincrsd and Anarihropord nioiiodon. In contrasl lo 

 what occurs in /•'/. scrnrifrons none of these species show a regular arrangement 

 of Ihe small plales, and in a nund)er of lluin (he laller appear in a very irreg- 

 ular and variable way, as they may appear logelher willi olher forms of calci- 

 licalion within the same colony, even on Ihe same wall. Time does not allow 

 me lo enler inio details, bul 1 will jusi meulioii Sniillimt Irispinosd. Iliislrd scrni- 

 Idid and /•'/. piscifiiniiis as examples of such si)ecies. While Ibe small plales in 



' Til, p. •_'!(;: .').'.. |> :t. 



