219 



only to a slight extent takes part in its I'oiniation in most species of the genus 

 Sciiticell<i. When the cryptocyst lamina expands on the inner surface of the frontal 

 wall the rihs grow at the same time from the hilaminar, uncalcified marginal 

 portion, in which the cryptocyst and the gynuiocyst meet, and they must there- 

 fore themselves be considered ])ilaminar, although the two layers in most cases 

 will he coalesced into one solid rib. In some cases e. g. in Scuticelln maryaritacea, 

 var. conneclens (PI. XX, figs. 3 b, 3 c) these spines, between which there is left a 

 part of the original sinus, remain uncalcified at the end, and this may be seen 

 most plainly in the gonozooeciuni. 



While the a})ove mentioned cryptocyst lamina is originally only continuous 

 with the margin of the primary aperture and is otherwise free (PI. XI, fig. 1 n cpl.), 

 it gradually with growth coalesces with the inner surface of the frontal wall to 

 a varying extent and in diiTerent ways; it is for instance distinctly seen in Costi- 

 celld lidsldla (PI. XII, figs. 1 a--l d. see explanation of plates) that the hollow in 

 the quadrangular, plate-like spines rising from the sternal sinus, is continued 

 bej'ond their starling point uj) to the round fenestrsc in the .sternal area. The 

 fact is that the regions, separating these hollow spaces from each other, are 

 formed by a fusion or soldering of the cryptocyst lamina with the inner surface 

 of the gymnocyst. 



With the exception of a few species (Cnlindiiim ornatiim, Piemcella (jemelki) 

 in which every internode consists of two or three zooecia, we find in the others 

 internodes with one and internodes with two zorecia alternating more or less 

 regularly with each other, but we may in this respect distinguish between two 

 cases, which do not however show any important differences, as both may appear 

 within the same genus. In one case a bizocrcial internode always takes its origin 

 from a unizoa^cial one, while here and there a series of successive single zonccia 

 may spring from the daughter-zoa^cium of a bizooecial joint. This is the case 

 e. g. in SciiticcUa j)hi(jlstnnut, Sc. intermedin, Sc. loiica, Sc. Wilsani, Sc. amphora, 

 Sc. iiKiciildla, Cribricclla riifa,Crib. crihraria, Cateiuiria pcrj'ornla. Cat. elegans and 

 Cat. formosa. In the other case one bizooecial segment may on the contrary often 

 follow another, which may be repeated at least three times, while at the same 

 time an alternation of uni- and bizooecial internodes may be seen in the neighbour- 

 ing branches. This may be seen in Scnticella ventricosa, Sc. margaritacca, Ptero- 

 cella alata, CUwiporelln gemiimta, Catenaria Buski, Cat. fiisca. Cat. taiiriiia and 

 Stropliipora Harueyi. 



